leaky boat

I'm just not sure that hull deflection is the reason my V11 is 12% slower than Rick's version. Marc calculated that I should be able to approximate the water pressure on the skin by placing a 2.5 ' long by 4" wide board with a 13 lb weight on the hull between the bulkheads and observe the deflection.

When I took a closer look at how much the skin deflected, I realized that it doesn't move at all on the curved part of the hull which is almost the entire hull aside from a small section of flat side walls under the water line. My water line is about 4" below the deck, and the amount of flat wall on the hull below 4" is only an inch or so. Even if that area was deflecting, it would represent a very small and possibly insignificant portion of the entire hull in the water.

To test, I was going to seal up the edges of the deck with fiberglass tape and epoxy, then pressurize the hull with air to stop the sides from deflecting. Easier said than done.

I had to seal the edges anyhow because they leak water when waves splash on deck, so I figured that it was a job worth doing regardless. After I had sealed up the edges, I hooked up my compressor and there are a million tiny air leaks through the flange where the deck is taped to the hull - the glas stape and epoxy didn't seal it air-tight. They aren't leaky enough to be concerned with much water getting in (that is good), but they do prevent me from being able to keep enough air pressure in the hull to do a water test for hull deflection. To go around and fix all the leaks would be a major pain and I just don't want to do it.

Many of you suggested placing air bags into the hull. Now that the top deck is sealed on, I don't want to cut it back out to place air bags in!

The other solution to deflection that has been suggested is to run some carbon reinforcement ribs longitudinally between the perpendicular bulkheads. Again, I would have to cut open the top deck to get in there, and I don't really want to bother with the effort and additional weight if it isn't really required.

Another idea suggested was to fill the compartments between bulkheads up with expanding foam. The reason I didn't leave the Styrofoam plug in the hull was to save weight. Foam would add substantial weight to the hull and I do not think this option is worth the additional displacement that the increased weight would cause. The hollow shell with the deck on weighs less than 20 lbs and if possible, I would like to keep it that way. Adding ribs wouldn't increase the overall weight that much, but I don't want to cut the deck open to add the ribs if they end up doing nothing to increase me speed.

I do need to surface finish the hull - especially the first 6 feet or so. The surface is a bit rough and a thin application of micro with sanding would smoothen it out quite a bit. With the deflection of the side walls, I worry about being able to sand it flat.

One option that I am considering is to tip the boat on it's side, drill a small hole in the opposite side, then pour in a small amount of expanding foam. This foam would settle against the side wall and could provide enough additional structure to stop any deflection without adding too much weight. At least it would give me a more solid hull to micro and sand smooth. I could limit this foam wall to the first compartment which is about 6 feet from the tip of the bow to the first bulkhead.
My new super-strong stainless steel u-joints arrived yesterday. Manny did some research and found me a new u-joint that didn't have the draggy flange on it, and was rated to take the torque. I contacted Curtis Universal and it turns out that the President is a kayaker and really digs what I am doing, so he donated two of them to the project! That's pretty cool considering they are worth $130 bucks each! Thanks Curtis!

You can see the difference between the two joints in the photo above. I doubt that the more hydrodynamic Curtis U-joint is worth the missing 12%, but it will certainly help.

The next step is to try to somehow stiffen the side walls near the bow, then apply some micro and do some sanding to get the surface finish of the bow area smooth. Rick Willoughby is in Canada on a vacation with his wife, and is swinging by Calgary on Tuesday of next week. He brought his stainless steel prop with him, and we can substitute my prop for his and run a test to see if the culprit is my prop. I took a closer look at the prop today and it is very easy to bend by hand. Perhaps a thin aluminum prop isn't stiff enough to press back on the water as it spins at 400 rpm.

I have a sneaking hunch now that my problems could be due to the prop. Either it is too thick (Manny had to thicken it a bit to cnc machine), or it is too flexy.

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6 Responses to “leaky boat”

  1. # Anonymous Anonymous

    Try a product called "NoTubes" sealant to seal your hull. You can "inject" it through your valve stem and it will seal all the holes you're talking about fairly quicky and easily. It's used for sealing regular bicycle tires so you can run them without tubes. It seals puncture holes as well as porous tire sidewalls so it should work for your application. has videos etc. You should be able to buy it from any bike shop.


  2. # Anonymous jan lietaer

    I would do a "tugboat tug force" test before drilling in the hull.


  3. # Blogger fhe

    What is interesting is that the two power curves are not exactly parallel. You do worse overall but it is more pronounced at higher power levels. That too would argue for the prop in my opinion.  

  4. # Blogger Adventures of Greg

    The spray-in latex sealant probably wouldn't work in this case, as the volume of the boat hull is considerably more than a bike tire.

    On the tug boat - good idea, but I think a small electric troll motor with an amp meter between the battery and the motor would be better. If I find that my speed at 100 watts using the trolling motor is higher than my prop, I know somethings up with the prop.

    It will still be easier just to use a known good prop - and that will be Ricks when he arrives next week.


  5. # Anonymous Anonymous


    I know that you have been getting lots of suggestions. Well, below are more. Sorry for the length and suggesting anything that you’ve already done.
    here are my ideas on equaling Rick’s boat:

    - Details are very important. That’s my main thought. Your hull drag is potentially very low. The whole boat will benefit from as much attention to detail as Rick put into the hull shape.

    - I agree that prop deflection might be a problem. Replace with steel or SS? Use tempered 4130 steel? The watts and speed and lift profile are known, so Rick could figure out how to load the prop and test it for deflection

    - In sailboats a smooth fair hull is very important. Same thing for airplanes. Same thing for your HPB. I would suggest the same tools and materials that are used on composite home built airplanes. Micro balloons mixed with epoxy make a good lightweight fairing filler. You can buy premixed lightweight fillers too.

    - I would fill the hull first with 2 part 2 pcf urethane foam. You have to take off the deck to do this, but with the foam filled hull you can use a very light deck. Sand the foam flat on top and apply the skin directly. Once you do this you can sand the hull without it deflecting too much. If your hull has 300lbs total buoyancy, the foam will add around 10 lbs to your total weight.

    - Why not blow off the u-joint and go with Rick’s bendy shaft? A strut adds drag. U-joints under load have friction, unless they are built with needle bearings, but needle bearing u-joints are big. The bending of the shaft is elastic, so in theory it consumes no energy.

    - An aero section profile has around 1/10 the drag of a round section. The leading edge is just as important as the trailing edge – maybe more so. A cylindrical or spherical nose has much higher drag than the true airfoil shapes that are closer to parabolic. The rudder should not have a cylindrical leading edge. It should be accurate full aero. If you have a good profile the rudder can be pretty small.

    - The fit of the rudder to the hull can easily add more drag than an entire aero profile rudder, so the fit to the hull should be very tight. This is high on the list too.

    - The nose of the prop hub should be an aero profile. Best would be a new stiffer SS prop that has a full aero hub shape nose to tail. Or, could the hub be the same diameter as the shaft?
    Now a few ideas on how you might beat Rick’s boat:

    - Machine down the sides of the rudder pivot shaft so that you can use a thinner rudder profile. Maybe a 3/4 shaft machined down to 3/8. You could probably go to 1/2 machined to 1/4.

    - Set the outriggers out of the water and add small angled foils under them. As one side drops that side gets extra lift and straightens you back up. I think you will be surprised how small they can be. I’d start with 5” clearance between outriggers and the water and use symmetric foils 10” long and 1.5” from leading to trailing edges. Play with the angle of attack by rotating the cross strut and the vertical angle to the water surface by bending the foils. You might be able to tweak the angle of attack as you pedal with a lever attached to the cross bar.

    - Can the outriggers and replace them with small light aero shapes. With the foils they should never touch the water and you get back a little of the weight gain from the foam.

    - Move the rudder to the front. You can only balance a bike by steering the front wheel. If this worked you wouldn’t need the foils, but you do need good steering and you might have to add a fixed skeg in back for stability. I’d suggest a small windsurfing foil for that.

    - I think you could lower your pedals. The water will be pretty flat. I think your feet could actually drop into cutouts in the hull at their low point. Pretty easy to do if the hull is foam filled. Cut out clearance and put a thin layer of composite over the exposed foam.

    - Or, cut down the whole hull. For a record attempt on flat water your freeboard – distance from deck to water line – is more than you need. This will reduce the weight penalty from foam filling the hull. Might be an easy way to remove the deck off too.

    Well, I hope there is something of use in here.

    Good Luck!


  6. # Blogger Adventures of Greg

    Peter: Those are all very good suggestions!

    prop: we are trying Ricks steel prop

    Smooth hull: I have already started the micro / sanding process

    Fill with foam: It will add too much weight and I think that the hull is stiff enough. When sanding the micro, I don't really see any noticable deflection.

    U-joint: Sprint steel is hard to find, but it may be worth trying to get some

    Rudder: yes, it should have a proper aero profile. That is on my list. And I also plan on making the fit to the hull tighter

    Small hydrofoils: not a bad idea, and something to play with once we get the speed up to where it should be. I might also think about replacing the floats with planing skimmers which weigh less rather than displacement floats.

    Lower pedals: I could gid a couple of grooves down into the hull for my heels to clear. I'd rather not, but it is something to think about.



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