Know Your Depths

Posted on December 9, 2013 by Don Gilzean

We had an opportunity recently to check depths in the mooring field at Ayala Cove and the docks at Sam’s Anchor Cafe. The results were surprising! At a zero tide:

  • Depths on the west and southwest sides of the mooring field (the side closest to the land) are 5 feet.
  • The middle of the mooring field is a pretty consistent 4 feet
  • The moorings located on the northeast side (the inside of the cove) have only 3.5 feet

Santorini and Orion draw nearly 6 feet, which means if you approach the mooring field from the normal direction in less than a 2.5 foot tide, you are going to get stuck! Here is a practical example. Tides for Saturday September 21 and Sunday September 22, 2013 indicate:

  • High at 1323 6.1; Low at 1935 0.3; High at 0218 5.2; Low at 0737 1.7

When you arrive at your northeast mooring ball at 1400, you will have over 9 feet of water … no problem. By about 1930, your keel will settle over 2 feet deep in mud which probably won’t be a problem because you plan on spending the night there (hopefully that motor boat beside you tied up to 2 balls, because if he only grabbed 1 he is going to swing all night and you aren’t). Unfortunately, at 0730, when you plan to leave to sail over to San Francisco for breakfast, you are at another low, and back to a foot deep in mud … in other words … stuck fast. Using the rule of twelfths (see below) to figure tidal changes, it will be about 0930 or 1000 before you have enough water to leave the mooring!

Sam’s Anchor Café is another location to be careful.  At a zero tide, there is 4 feet at the end of the left dock, and 3.5 feet at the end of the right dock.  Half way up the docks, there is 3 feet on the left dock and 2.5 feet on the right dock.

Now for the tip …

First, know your draft, and how your depth sounder reads compared to actual water depths. The only way to be sure of that is with a lead line. A simple one can be made by tying a 10 or 12 oz. round lead fishing weight to a 25 or 30 foot light weight line. Mark the measurements on the line (mine has a mark every 6 feet, with the last 6 feet marked in 1 foot intervals). Lower it into the water beside the boat to get an actual measurement of depth. Compare that to the depth sounder on the boat. If the line indicates 16 feet of water, the depth sounder shows 10 feet, and you know you have a 6 foot draft, then the sounder is reading from the bottom of the keel, and you have 10 feet of water under it.

Second, know what the tides are doing! Not just the highs and lows, but what is happening in the middle. After all, rarely will you arrive or depart right on the extreme. A good general rule to follow is called the Rule of Twelfths, which basically says 1 twelfth of the tide change will take place in the first hour after the high or low. 2 twelfths of the change will happen during the second hour, 3 twelfths during the 3rd and 4th hours, 2 twelfths during the 5th hour, and the final 1 twelfth during the sixth hour. Sounds challenging, but is actually pretty simple. For example … using round figures, lets say the tidal change (low to high) is expected to be 4’. 4’ divided by 12 equals 4”. At the 0800 low tide, you have 2’. One hour later (0900) you should have about 2’ 4”. One hour after that (1000) you will have about 3’. At 1100 about 4’, at noon 5’, at 1300 5’8″, and at 1400 6′. It’s not exact, but it will get you pretty close.

When you tie up, check your depth (use the lead line if you don’t have a working depth sounder you trust). Compare the depths with what will happen to the tide during your stay. Get out before the water goes away! If I have a 5’ draft with 5.5’ of water and a falling tide, I’m going to find somewhere else to go.

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C’mon, It’s Not All Bad!

Posted on November 4, 2013 by Craig Walker

C’mon, it’s not all bad!
Here’s another chapter from Captain Craig’s offshore journal. Okay, okay, a few folks might have been a little spooked by my article on scariest moments outside the gate. Remember, these are only ten stories from over a hundred trips outside the gate. All those trips that went exceeding well are perhaps a lot less exciting but, as I said in my last article, wonderful times can be had if you are well prepared, watch the weather forecast, can handle the idea of solving problems if and when they arise and don’t get complacent. Really these are good rules to follow inside or outside the gate.
So, what about the good stories? As I said, these are usually less exciting. I do know that it was the good memories from my first trip to Hawaii that made me want to do it again. I call this selective amnesia. I remembered the beautiful sunsets, the moon lit nights with fabulous stars, cruising at 8 to 10 knots with a spinnaker and perfecting my downwind driving during the day so that it was a no brainer at night. The celebration at the half way point and the exhilaration of sighting land were really fun too. So, those fond memories outweighed the “challenges” that we also faced racing to Kaneohe Bay.
Selective amnesia seems to work well regarding my trips out the gate too.
When doing the Half Moon Bay to Drakes Bay loop, I have to admit that going south has been more fun and relaxing. A nice broad reach on the ocean makes for some fun steering and the legs are long enough for everyone to have a “trick at the wheel”. If you haven’t heard that phrase before, look it up. That’s a good ‘ole nautical phrase. I’ve learned that when making the “loop” you’re usually better off going to Half Moon Bay, then Drakes Bay and then home. If you haven’t taken Tradewinds Advanced Coastal Cruising Class (ACC) yet, your instructor will discuss why this is the case.
Visiting the rough and tumble fishing boat port at Pillar Point Harbor in Half Moon Bay is always fun. We usually have a great meal at the Ketch Joanne, Barbara’s Fish Trap or Half Moon Bay Brewing Company. Have you tried a Big Break Ale, Matt? (edit: Of course I have! I LOVE HMB Brewing…) A short walk into the quaint little town of Princeton By The Sea, is fun also.
Going north has its moments also. There are several options for going north on the California coast. Keep in mind that the prevailing winds are from, guess what?, right where you want to go. Your options are motoring, motor sailing or a lot of tacking. For me, it has been a fun challenge to maximize tacking efficiency. But this requires a fair amount of planning, patience and perseverance. Did I mention motor sailing? Hopefully, you all caught that. Once again, in ACC class you’re going to learn that motor sailing, when done properly, can be a very important component when going north on our coast. And, please be mindful that Tradewinds policy is no motor sailing inside the Bay.
If you motor out to the Farallones from Half Moon Bay early in the morning when the winds are light, you’ve set yourself up for a beautiful reach into Drakes Bay in the afternoon with plenty of light left over anchoring and firing up the BBQ. Drakes Bay can be quite idyllic. It is well protected from NW swells even though it can be quite windy. The landscape is spectacular with its white cliffs and colorful rock formations and sparse enough to imagine what it must have been like when Sir Francis Drake careened his “Golden Hinde” there in 1579.
Rounding the Farallones gives one a great sense of accomplishment but, if you’re expecting a beautiful island with palm trees, you may be a little disappointed. After all, they are just big treeless rocks on the edge of the continental shelf. Still, it’s fun sighting the islands, rounding them with a wide margin and saying you’ve done it.
Remember those sunsets and starry nights I mentioned earlier? I’ve had my share of those, right here on our little coast. Sea life is abundant also: whales, dolphins, porpoises, sea lions, harbor seals, flying fish, pelicans, frigatebirds, shearwaters, scoters, gulls, huge jelly fish, etc., etc. I always bring my field guides!
I’m not a fisherman. Sailboats and fishing lines don’t seem to pair together very well unless you’re going to sail in a straight line for a good while. We caught a lot of fish going to Hawaii and I know there is good fishing on our coast too. Just ask Elvis. Elvis runs a fishing charter boat and hangs out at Tradewinds from time to time.
Surf’s up! Coming back into the gate on a run with a following sea and flood tide can be a real kick. I can remember surfing a Catalina 38 with speeds up to 18 knots. Of course this was with a Spinnaker and a Blooper and the timing was well planned. Do they still make Bloopers Angie? (edit: Kinda…. but they are horribly out of style…)
This was tricky work but great fun. You can do the same with just the main and jib, wing and wing. You’ll have the skills at the ACC level to control the boat in following seas, being mindful to avoid the jibe. Enjoy the ride!
Hopefully, these comments will inspire some interest in sailing the Gulf of the Farallones!
Fair winds.
Captain Craig

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What’s in a Gust

Posted on October 28, 2013 by Don Gilzean

A few days ago I was checking the weather forecast for that day on San Francisco Bay.  It was a pretty mild wind forecast for late August, winds from the SW at 15 with gusts to 25, however it got me thinking about what that really meant.

Winds from the SW at 15 … wow … the perfect wind for sailing under an un-reefed main and full jib.  But, what about those gust to 25?  Here are a couple of things to keep in mind about wind in general and gusts in particular.

First, the difference in the power of the wind is not just 10 knots (a 66% increase).  The power of wind doesn’t increase in a straight line, it increases exponentially.  25 knots of wind contains nearly 300% of the force of a 15 knot wind.  That well balanced 15 knot sail plan is way over powered in 25 knots.

The second thing to keep in mind is wind direction.  Although this can be altered by the geography of the bay, in most cases, gusts come from the right of the wind’s true direction.  In other words, that SW 15 wind may be gusting at 25 from the W.  If you are on a port tack in the gusts your sails are probably “under trimmed” based on the wind direction, which may be a good thing while you ride out the gust.  On the other hand, if you are on a starboard tack, when the gust hits, you are over trimmed in 3 times more wind!  No wonder things get a little hairy out there during gusts.  One last thought regarding the starboard tack idea … what is going to happen if you are on a run before the gust overtakes you?  At best, you will be sailing by the lee … at worst; the gust gets on the wrong side of the main sail, and WHAM!  An accidental jibe in 25 knots can ruin an otherwise perfect day of sailing!

So, here is the question.  In those conditions, do you reef, or not?  Unfortunately, the answer is not a simple yes or no.  How many gusts are there?  How long are they lasting?  What is my tack and point of sail?  I do know that I am more likely to reef if I’m on a starboard tack with the wind forward of the beam and less likely on a port tack or with the wind abaft the beam.  I probably won’t worry too much about being on a run on a port tack, but will rarely go on a run on a starboard tack during gusty conditions.

It basically boils down to this … if I find myself (or someone else on the boat) asking “should I reef?”  The answer is YES!!  It’s very easy to shake it out later if I didn’t really need it.

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Capt. Craig’s Top Ten Scariest Advanced Coastal Cruising Stories

Posted on September 17, 2013 by Craig Walker

September 2013

Introduction:
So… why I am sharing these stories?
As we turn more instructors and members loose to sail “outside the gate”, I think it is important to share some important hard-earned lessons about sailing in the Gulf of Farallones. You’ve read the stories in Latitude 38 about recent tragedy. Most, if not all major mishaps could have been avoided. We all learn from experience. I’ve been teaching Advanced Coastal Cruising since 1992 and sailing those waters on my own since ’76. I probably have at least a hundred trips under my keel and I’ve learned important lessons on almost every voyage.
What are the key take-aways? They are: Be very, very well prepared, you must learn how to be a problem solver and don’t ever, ever get complacent. If you can do these things, you’ll wind up safely enjoying the challenge and beauty outside the gate.

Top Ten Scariest Advanced Coastal Cruising Stories
1. Boat: Hylas 44, Location: 4 miles southeast of Chimney Rock, Time: 2230, Winds: NW 35 to 40 knots, Seas: 12 to 14 ft – Steering Failure! The boat rounds up into irons and starts to broach. Everybody has PFDs, harnesses, tethers and attached to jack lines. We work on getting both sails down and lying-ahull. Upon inspection we determine that two steering cable pulleys have pulled out of rotted plywood mounts. We locate the emergency tiller and find we have to cut a hole in the headliner for the tiller to connect to the rudder post. I should have made sure I understood that before we left! The guys get a good lesson in steering a boat with an emergency tiller as we motor through rough seas and into Drakes Bay for anchoring and rest before our trip home.
2. Boat: C&C 40, Location: Chimney Rock at the entrance to Drakes Bay, Time 1830 (Summer), Winds: Light Westerly, Seas: less than 5 ft. – Navigating by Braille! -We’d plotted a nice course into the Bay from the Green No. One marker buoy. Unfortunately, the ebb tide was very strong and kept pushing us to the west. Going about 6 knots under power, we had a close encounter with Chimney rock, bouncing very hard on a submerged rock. After getting into the Bay and getting a hook on the bottom, we started a rigorous inspection looking for signs of hull damage. We found a slow leak next to cracks around the keel bolts and cracked fiberglass where the backstay tensioner was located. We determined we could motor safely back to SF if the seas were calm. We developed some contingency plans about calling for assistance and maintained a constant watch on the leak as we motored home at first light the next morning. Attention Coastal Navigators – this would have been a great opportunity to use the Danger Bearing.
3. Boat: Jeanneau 43, Location: At anchor in Drakes Bay, Time: 2300, Winds: W 25 knots, 35 knots and then 40 knots – A very long night! After a rough trip into Drakes Bay, predicted winds keep building. Winds were forecast to drop off after midnight but just kept building until 5 AM. Drakes Bay has grassy spots and “Whale Song” has a Bruce anchor as primary. These anchors don’t hold well in grass. If you’re going to Drake’s, you better have a plow anchor. This is the same day that one of my crew became hypothermic and we still had four hours of tacking to get into our anchorage. (Instructor tip: use your students to keep the anchor watch, you probably still won’t sleep, but students need to understand the importance.)
4. Boat: C&C 40, Location: 5 miles south of Drakes Bay in about 200’ depth, Time: 2100, Winds: West 20 knots, Seas: 6 ft. – Crab Pot! Crab pots are plentiful around the 200 ft. depth contour in season and, unfortunately, abandoned pots stay out there all year. It is hard enough to see them during the day and impossible at night. On one of our trips during night time man overboard drills we snagged a pot on the rudder and came to a soft stop. We immediately got our sails down. At least conditions were not miserable. We were snagged for several hours trying to free the line with a boat hook and anything else we could think of. Later we tried various sail combinations to try and sail off. Since we didn’t know if the line also snagged the prop, we stayed completely away from the idea of using the engine. We were able to turn the prop by hand in neutral, though. With enough wave action we finally were able to grab enough line to cut through. On another trip, we snagged a pot and just floated free in about twenty minutes.
5. Boat: Jeanneau 43, Location: half mile east of Southeast Farallon Island, Time: 1300, Winds: W 25 knots on nice beam reach, Seas: 6 ft. – “There be whales here!” I used to ask the universe to see whales up close. I also used to promise my students that we would see whales on every trip offshore if we looked hard enough. On one trip north we encountered a pod of at least fifty Gray whales, coming every which way including straight at us. We had several surface right next to the boat and one surface right in front of us. I am sure that that particular whale looked at me eyeball to eyeball! This was exhilarating but at the same time very precarious. These whales generally follow the 100 fathom line and can be seen all year long in the Gulf of the Farallones. I no longer go out of my way to go near whales. In fact there are official advisories about not doing this. I also turn on the engine so that the boat makes a little more noise but I’ve never seen any evidence that this makes a difference. I think a sailboat is fairly insignificant to these great creatures. I haven’t heard of an actual collision with a whale in our waters recently but I recommend giving them wide berth.
6. Boat: Hunter 36, Location: Smack-Dab in the middle of the Potato Patch, Time: 1400, Winds: W 30 knots, Seas: 20 ft – Roller Coaster! Before I knew better, I occasionally found myself in the Potato Patch, a.k.a. Four Fathom Bank, a.k.a. the North Bar at the entrance to San Francisco Bay. So… what happens when you have 15 to 20 ft. seas piling up against 4 fathoms (24 ft of water)? The answer is a wild and very dangerous ride. With only a jib, our little 36 ft. boat was making about 14 knots and barely controllable with a steep quartering sea. Never-never do this! In fact, please, just stay out of the Potato Patch as a matter of habit.
7. Boat: Ericson 39, Location: Somewhere between the Farallones and Drakes Bay, Winds: NW 25 to 30 knots, Seas: 6 to 8 ft. – Man the bilge pumps! It’s always a little disconcerting to go below when offshore and find a foot or two of water sloshing around your feet! On top of the water we also found a visible sheen of diesel fuel. The water got pumped out and we made it safely into Drakes Bay. With flat seas the next morning we had a safe return to San Francisco Bay. Tony Johnson can tell us where that water came from! This boat was his “Maverick” and went on to circumnavigate the globe!
8. Boat: Jeanneau 43, Location: north of the Main Ship Channel in between Pt. Bonita and the Golden Gate Bridge, Winds: W 10 knots, Seas: < 2 ft. – Fog! Unfortunately, I have too many fog stories. The scariest was coming back into the Bay one morning. We had purposely stayed way North of the Main Ship Channel to avoid commercial traffic. We were getting intermittent contacts on our RADAR which wasn’t working properly on this trip. We hadn’t been monitoring Channel 12 or 14 because we came home via the Bonita Channel. From the pea soup fog, two large tug boats emerged on either side of us within 100 yards each. That’ll make your hair stand on end. RADAR… don’t leave home (the Bay) without it. Even better, take Bill Yawn’s ASA RADAR class.
9. Boat: Jeanneau 43, Location: Way too close to Colorado Reef, Time: 1530, Winds: S 15 knots, Seas: 2 to 4 ft. – Mavericks Anyone! It’s usually a reach down to Half Moon Bay from San Francisco with prevailing Northwesterlies. On this day we had winds from the south and had the pleasure of tacking. One particular tack took us way too close to shore, about half way between Pt. Montara and Red Buoy “26”. Check the chart. This is just north of Colorado Reef and famous breakers of the “Mavericks” surf competition. This is no place for a sailboat. This was a good lesson for the instructor who was dazed by a good dose of the sea sickness medicine called Stugeron and relied too heavily on his student navigators to keep the boat safe.
10. Boat: Jeanneau 43, Location: 2 miles west of San Pedro Rock, Time: 1730, Winds: NW 25 knots, Seas: 5 to 7 ft. – Anyone wearing a belt? We were enjoying a nice reach on moderate seas and running the engine to keep the RADAR juiced up when the engine alarm went off. Oil pressure dropped to zero. Opening the engine compartment, we got a nice surprise. Oil everywhere! After a frantic search we found the source of the problem. The oil filter had worked itself loose. How can this happen? The engine had just been serviced and when the filter was replaced, the gasket wasn’t seated properly. You could see how it was deformed. Next question… do we have oil? How about a filter wrench? Fortunately, there was oil but no wrench. One of my students volunteered his leather belt and we replaced the filter well enough to power into Pillar Point Harbor. Then… the massive clean-up effort!

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Plimsoll Line

Posted on September 9, 2013 by Tony Johnson

Remember when you were just learning to sail and the boat heeled over for the first time? My instructor was calm, but I’m told I was yelling “Help! Yikes! Eeek!”…although I’m pretty sure it was quite a bit more dignified than that. From ancient times to the present, this feeling that the boat might capsize or sink has been, well, a concern, for good reason. It’s the space age, and boats are still going to the bottom.
The Cretans established guidelines for loading boats as early as 2500 BC, but it wasn’t until 1930 that there was an international agreement on the standards developed by an Englishman named Plimsoll in the 19th century. That circle with a line through it next to a sort of ladder graphic that you see on the hull of the Red Oak Victory is the result. This represents the waterline maximum that the ship can safely be immersed to, depending on season and salinity represented by the various horizontal lines.
So what’s safe for our sailboats?
The Net Register Tonnage of Tradewinds’ Lionheart is 5.49, which means the volume that can be used for cargo or passengers is 549 cubic feet. The weight of this volume of water is 549 x 7.5 [gallons per cubic foot] x 8.333 [weight of a gallon of water] = 34299 pounds. So if the boat itself weighed nothing and it was filled with water, the volume of the boat would displace 34299 pounds of water. But the empty boat already weighs 9170 pounds, so if we subtract that from 34299 we get 25129. This is equal to about 405 cubic feet or a little over 3000 gallons or roughly ¾ of Lionheart’s interior volume. So if we fill Lionheart with 3000 gallons of water, she will weigh the same as the surrounding water and sink. But this assumes a perfectly stable, flat sea. Boating enthusiasts have adopted a much more conservative rule of thumb for capacity of passengers which you will recognize: length times beam divided by 15. On Lionheart this gives a capacity of 20, which is quite a bit more than you’re likely to have aboard. If we assume 184 lbs per person, we get a total of 3680 pounds, about 1/7th of what it would take to sink the boat. The other 6/7ths represents her reserve buoyancy, allowing that heeling, and downsizing my “Eeek!” to “Yow!”

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Skipper’s Tip – Corrosion & Equipment Failure

Posted on August 13, 2013 by TW-Matt

It’s been said around Tradewinds that there are many things on a boat that can be fixed with liberal application of fresh water. Here are a few of our favorite examples of why that is true – please consider them next time you put a boat away:

1. Windlasses – we are often called upon to repair a non-functioning windlass. The solution 90% of the time is to dis-assemble, clean, grease, and reassemble it. What we find is salt – lots and lots of salt crusting the base and the making the moving parts not want to move so well. Our research (speaking to members) shows that the windlasses are rarely used – people anchor on our boats occasionally, but not often. Almost every time you sail, salt water is coming over the bow, washing the fore-deck, and sloshing over and around the windlass. Don’t forget to open the locker (whether you anchored during your trip or not) and rinse with fresh water – that way next time you do want (or need) to anchor, that windlass will do it’s job for you.

2. High hardware – OK, it’s not the highest hardware on a boat, but there are plenty  of blocks, bails, lines, and miscellaneous parts that are attached to the bottom of the boom or near the boom on the mast. These get covered in a nice layer of salty air and spray when you sail. Imagine how well they get rinsed if the mainsail cover is already on when you spray down the boat – not so much! Don’t forget to look a little higher and get these spots rinsed before putting on covers. This goes for binnacles as well.

3. Zippers – The mainsail cover and binnacle covers are typically inside when you sail and don’t receive spray, but the same cannot be said for the dodger and bimini hardware. We find that in particular, the inside of the dodger zippers is not getting rinsed and corrodes faster that the outside. Be sure to get that hose in the cockpit and up under the dodger panels, soaking the zippers well. Don’t forget clutches, fair-leads, and other hardware that is under the dodger.

Sure, it’s great to wash down the boat for the sake of cleanliness, but don’t forget it’s also an important part of boat maintenance. Getting the salt out of all of the parts is critical to their long life. Any hardware, stanchions, lifelines, running rigging, standing rigging, anything that gets exposed to the salty spray of the bay, needs the liberal application of fresh water after every single sail to keep it in good operating condition.

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Beware the Lee Shore!!!

Posted on August 6, 2013 by Don Gilzean

We have all heard it and all believe it, but really, what is a Lee Shore. Its not just the “land” to leeward … it’s also the row of boats behind you as you back out of an upwind slip. Its the row of boats next to you as you back out of a down wind slip. It’s “big boat row” as you exit D Dock. It’s the Red Oak Victory Ship as you round the corner into the reach.

Regardless of what it is, stay as far away from it as you can!!!

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Crew Overboard Practice

Posted on July 30, 2013 by Don Gilzean

You can never practice crew overboard recoveries too much! If a real crew overboard happens you want instinct and “muscle memory” to take over. Only practice will get you to that point. For a bit of extra practice try cleaning the bay. Next time you sail past a piece of trash floating in the bay, check for safety and conduct a crew overboard drill. Carrying a small net may help with some of the trash you find. Chances are you will never be at a loss for opportunities, and you will hone your and your crew’s skills, cleaning up the bay at the same time.

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Watch the Stern

Posted on July 16, 2013 by Don Gilzean

First a “tip” then the detailed explanation with some practice exercises.

The Tip: While docking in a slip (once the bow is in the slip) and when doing a fairway rotation, focus primarily on where the stern is with observation sweeps forward to ensure safety of your boat and crew.
****************

The Detail: Next time you are sitting on the patio enjoying a break after the day’s sail, pay a bit of attention to the returning boats pulling into their slips. I used to be amazed at how often the boat would be half way into the slip when it’s brought to a stop, then the helms person has to “push” it the rest of the way in. Depending on wind direction, this can be easy, or down right painful. There are a number of reasons this happens, however, here is one of the biggest.

With any boat, there is a blind spot in front of the bow. A container ship’s blind spot can extend for a quarter of a mile in front of the bow. With the sailboats in our fleet, it’s not unusual for that blind spot to extend nearly the length of the boat. Which means, almost as soon as the bow is in the slip, the end of the slip begins to disappear under the bow. It doesn’t take long before it gets hard to judge position in the slip and the boat is brought to a stop … usually too soon, although occasionally it can be too late.

Here’s how to stop that.
1. Before departing the slip, make a mental note of where you are standing in relation to something on the dock finger directly beside you … the stern cleat for example.

2. Also before departing, make a note of where the main dock meets the gunwales on each side. With an unfamiliar boat, you might even put a spot of blue painter’s tape at the location on each side.

3. While returning to the slip as the dock begins to disappear under your bow, start watching the stern more than the bow. Look for that dock cleat at the stern of the boat. It’s much easier to judge speed and distance in relation to it, than to the dock in front of you. Don’t ignore looking forward, it’s important to know what’s happening up there. Try looking at the stern cleat relationship for 4 or 5 seconds, the glance forward for 2 or 3 seconds. If you do, you will be able to hold the boat in place, rather than the 5 foot forward/backward surging you often see.

While we are on the topic of watching the stern more than the bow, try doing the same during a fairway rotation. Say you are on a 40 foot boat in a 60 foot fairway. As you start the rotation, the stern is going to be close to the edge of the fairway, 5 or 10 feet maybe. The bow is 50 feet or more from the other edge. It’s much easier to judge distance at 5 feet away than at 50 feet away. As the turn gets get going, the bow swings closer and closer to the far dock. If you spend all of your time watching the bow, the tendency is for the boat to drift further and further towards the bow side of the fairway. If that side is to leeward, you have now placed yourself against a leeward shore, and you are in danger of getting pinned against the boats on that side.

Instead, as you do the rotation, watch the relationship of the stern to the dock. Keep it at 5 feet, and the bow will never get closer than 15 feet in the above example. And, you can tell when 5 feet becomes 10 feet. Use astern propulsion to keep you back … then, once the 5 foot relationship has been restored, go back into forward and let the prop wash take you the rest of the way around. Again, focus primarily on the stern, with safety/observational sweeps forward.
Instead of trying something new in close quarters, practice this maneuver out at the practice buoys in Marina Bay. Start by using the most wind sheltered buoy, turning to leeward and to windward, and then move to the ones more in the wind so that you can see what happens in varying wind conditions.

With any boat, there is a blind spot in front of the bow. A container ship’s blind spot can extend for a quarter of a mile in front of the bow. With the sailboats in our fleet, it’s not unusual for that blind spot to extend nearly the length of the boat. Which means, almost as soon as the bow is in the slip, the end of the slip begins to disappear under the bow. It doesn’t take long before it gets hard to judge position in the slip and the boat is brought to a stop … usually too soon, although occasionally it can be too late.

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Boat Handling Under Power – Part 2

Posted on June 25, 2013 by TW-Matt

Hopefully, by now you have done the boat exercises in Part 1.  If so, you know the “advance” and “transfer” associated with your favorite boat. You may have noticed that advance and transfer is different while turning to starboard than while turning to port.  Maneuvers in forward may show only slight differences, while maneuvers with astern propulsion may be quite different.  Part of this is the impact of wind, however, a great deal of the difference is attributed to the effects of propeller generated current on the boat.

 Propellers and Rudders

It doesn’t matter if the propeller is turning in a direction to move the boat forward or astern, current is generated.  Current moving across the blades of a propeller results in lower pressure on one side of the blade than on the other.  The blade (with the boat attached) pulls itself into the lower pressure.  Just like a sail pulls a boat forward into the wind. The turning propeller creates a current moving towards the propeller, referred to as “suction screw current”.  Moving away from the propeller, in a much more forceful, focused direction, is “discharge current”.  When you learn to manage these two types of current, especially the more forceful discharge current, and a third force known as “unequal blade thrust” your close quarter boat handling skills improve dramatically.  These three forces, alone or in combination with each other, result in what we generally refer to as “prop wash” and “prop walk”.

Prop Wash

Prop Wash is primarily a result of discharge current.  The greatest example of prop wash is found while the boat is not moving through the water.  Water flow across the rudder is required for steering control.  Sitting still in the water the rudder has little impact except as a large inefficient paddle.  As a boat begins to move through the water steering is gained and control over direction of travel is established.    However, there is another way to get current flowing across the rudder.  Because a rudder is mounted aft of the propeller engaging the propeller in forward produces a focused stream of water flowing directly across the rudder in the form of discharge current.  Turning the rudder causes higher pressure on one side of the rudder than the other, resulting in lift, and forces the stern to move towards the side with lower pressure.

It’s time for a small detour.  I often hear, and even say it myself, that “driving” a boat with a wheel is just like driving a car.  It gives a new helms-person confidence to do it.  The truth is, while the effect may seem similar (i.e. turn the wheel to the right and the car/boat turn to the right) the mechanics are totally different.  A car steers from the front wheels, with sideways (lateral) resistance created by the rear wheels.  A boat steers from the stern, with the “center of lateral resistance” located up at the keel (don’t worry; this isn’t a technical discussion of CLR).  Here’s the difference, with a car the back wheels follow the steering wheels.  With a boat, the bow moves opposite the stern, because the boat is pivoting on the CLR up at the keel.  Driving a boat in forward is actually more like backing a car in reverse.  The key point to know … a boat pivots on its CLR.

Back to the topic at hand.  Here is an exercise for you.  To test the impact of prop wash; pick a day with little or no wind.  Use a boat that you know has port prop walk.  In a slip use spring lines fore and aft from cleats located amidships, port and starboard.  That’s four lines starting amidships, one traveling forward, one aft, on each side of the boat.  Remove the bow and stern breast lines.  Make sure the boat cannot drive forward and strike the dock, dock box, or fire hydrant, and that it cannot accidentally back out of the slip.  In other words, make sure the boat is secure before starting.  Center the rudder.  Place the boat in forward at idle, and slowly turn the wheel to port.  The stern slides to starboard forcing the bow to port. Now, center the rudder … not much should happen (assuming no wind).    Turn the wheel to starboard until the “turn” stops.  Center the wheel.  This time, the stern may start to slowly move back to starboard due to the impact of unequal blade thrust which we will cover next.  As you can see, prop walk has a large impact on a boat sitting still in the water.

Here is how discharge current, suction current, and unequal blade thrust interacted in this exercise:

  1. Discharge current was the main player.  Water moving across the turned rudder caused the stern to move toward the lower pressure area, and the bow to pivot to the opposite direction.
  2. Unequal blade thrust.  Tried to slowly move the stern in the direction of propeller travel.  Was greatly overpowered by the discharge current while the rudder was turned.  Became more important at the rudder straightened.
  3. Suction current.  Water moving evenly across the hull and keel acted as a minor stabilizing force, however, was easily overpowered by both discharge current and unequal blade thrust.

Prop Walk

Prop walk is a combination of unequal blade thrust and discharge current.  The angle of the propeller shaft causes the “pitch” (in simple terms … the angle) of the propeller to vary depending on if the blade is descending or ascending.  The blades have a greater pitch while on the down side of the stroke that while on the up side.  In other words, a propeller turning clockwise is more efficient on the right side (down stroke) than it is on the left side, resulting in the stern wanting to “walk” to the strong side.  Most propellers turn clockwise in forward, and counter clockwise in reverse.  While in forward, the stern wants to go to starboard.  While in reverse, the stern wants to go to port (the first half of port prop walk).  The greater the shaft angle, the more pronounced the effect.  Now add in the impact of discharge current.  As the propeller turns counter clockwise (in reverse), the blades on the left are throwing water forward and down.  The blades on the right are throwing water forward and up … right into the curvature of the hull, creating greater pressure on the starboard side than the port side, forcing the stern to port.  Unequal blade thrust and discharge current both pull to port, and until you can get enough current over the rudder in the form of speed, you are not going to have control … unless you actually want the stern to move left (as in a fairway rotation).

Here’s part two of the earlier exercise.  Center the boat in the slip with the rudder centered.  Place the boat into reverse at idle.  The stern will move to port.  Turn the rudder to port.  Not much happens.  Turn the wheel to starboard.  Again, not much happens.  There may be a slight easing of the force to the left, due to suction current over the rudder, however, probably not enough to really make much difference.

It’s time to get out of the slip and into sheltered open water to put it all together.

Do four “fairway rotations”

  1. Forward turning clockwise
  2. Forward turning counter clockwise
  3. Astern propulsion turning clockwise
  4. Astern propulsion turning counter clockwise

Here are a few tips.  While turning clockwise, prop walk is a major contributor.  Balance it and prop wash for the most effect.  While turning counter clockwise, prop walk will stop your turn.  Eliminate as much of it as possible, and use prop wash as the major contributor.  You can’t do a fairway rotation while moving backwards.  Bring the boat to a stop with a centered rudder.  Then turn the rudder in the direction you wish to rotate, using prop wash to start the process moving.

Docking with prop walk.  Find a dock where you can safely conduct this next maneuver.  Under normal Marina Bay wind conditions, I like to use the leeward side of the D dock pump out station, port side to the dock, facing out.  Approach the dock at a 45 to 90 degree angle, slowly but with steerage way.  Stop the bow of the boat within two or three feet of the dock with the port side bow cleat near a dock cleat.  While the boat is resting in the water, the bow line handler should get the bow line around the dock cleat, and secure it back on the boat.  Make sure the dock line is NOT over any lifelines or pulpit rails.  DO NOT TRY TO HOLD THE BOW DOCKLINE by hand.  You can’t.  Secure it in a way it can be easily adjusted, and keeps hands and fingers clear!!!  After the bow line is secure, place the boat into reverse and slowly take up slack in the line.  Once the slack is removed, the stern will begin to walk slowly toward the dock.  Use only enough engine speed to keep the stern moving.  When close enough, get a stern line onto the dock, and secure the boat.  This maneuver works great in tight spaces with a boat in front of and a boat behind your docking location.

Departing a dock with prop walk.  Tie up starboard side to the dock.  Set up the bow line so that it can easily be released from the dock cleat while still on the boat (e.g. doubled around the cleat and back to the boat).  Center the rudder.  Release the stern line.  Engage reverse at idle, and allow the stern to prop walk away from the dock.  When clear, release the bow line and back away.  This is a great way to get away from the windward side of a dock with limited space fore and aft.

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