Whaleback Proa
Your bottom paint seems to go horendously high on the sides!!!
How heavy is your boat? Really?
How have you calculated the displacement of the main hull, to figure out how far it is going to sink when you put it in the water?
WIth vertical sides like your boat, it is not that complicated to approximate.
Imagine you “slice” your boat in, let’s say 3 ft sections. You start from the transom and go forward by 3ft increment. For each station, measure the beam and the height of the bottom paint on the side of the boat. Do the same thing at the transom.
Once you get the surface area of the transom (beam at transom x bottom paint height at the transom, measured in feet), and the surface area of the next station (same calculation as above), average the 2 figures, and multiply by 3ft, the distance between both stations. That gives you an APPROXIMATE value of the volume of the aft 3ft of the boat which is supposed to be under water.
Repeat the same calculation for each 3 ft section until you get to the stem. Average the surface area of front and aft sections below waterline, and multiply by 3 ft.
Add it all up, it will give you a displacement in cubic feet. Multiply by 7.48, it will give you gallons.
Multiply by 8.32 lbs/gal, it will give you the displacement in fresh water.
I bet you will end up with a number well above a ton…
Is your boat that heavy?
I hope for you that the true waterline, once floating, will be actually at least one foot lower than the top of the bottom paint.
Laurent
The design waterline was from the bottom of the transom to the bottom of the stem. That was with 400 lbs of ballast included in the calculation. I think I designed it with 1200 lbs total weight (perhaps 1400 lbs) when it was designed as a sharpie. I do not plan to ballast it as a proa.
I went back to my old .hul file from 2004 and found that 900 lbs is the displacement at the line between the bottom of the transom and the bottom of the stem. 1200 lbs is a few inches above that, and I think that was my design displacement. 600 lb boat, 200 lb pilot, 400 lb ballast/stores. That was entirely a guess at the time.
As an unballasted proa, it is likely that some of the flat bottom will be above the waterline, which would make the hull a bit slappy as waves hit it. However the boat will likely have a displacement in excess of 900 lbs when loaded for cruising, which should put the chines under the water. I have no idea how much it weighs empty but I would guess 400 to 500 lbs? The bottom is laminated up from plywood and is about 1-1/2” thick. The sides start at 1/2” at the bottom and are 1/4” at the top. The thick part (double laminated 1/4” ply) is painted with bottom paint. When I built it I expected to have to ballast it heavily, so I built the bottom heavy.
The bottom paint was painted on to cover the double lamination, not to show the waterline. I thought it was prettier that way.
Construction complete
The paint is dry, now just need to break it down into trailering mode.
This looks promising!
I hope you get your tacking proa into the water soon.
Cheers,
Johannes
I finally got the boat in the water. It takes about an hour and a half to lash it together. I had a few mishaps, my new motor conflicted with my tiller arm, so I will have to change it. I removed the tiller arm and did not have a rudder. For some reason there was no gas in the motor so I had to paddle upriver about a mile. Luckily I got some help and a tow for about half way. The boat did not paddle easily, although I may have been fighting current. I finally made it to the dock. Good thing there was no wind, or very little.
It floats quite high, the chines are an inch or two above water when it is empty. The cockpit well was too small for the Honda 2, it is larger than my old Johnson 2.
So I need a tiller before I can use the boat. More boatbuilding! shouldn’t be too hard.
Congrats on launching! You’ve completed the hardest part.
Whaleback Proa - Docked
http://www.youtube.com/watch?v=6u81QJo0iGg&feature=youtu.be
It is in the water, I am putting things together to get it ready for a first voyage.
Whaleback Proa - Docked
http://www.youtube.com/watch?v=6u81QJo0iGg&feature=youtu.be
It is in the water, I am putting things together to get it ready for a first voyage.
The video is marked as private. You will need to change the settings to public for us to see it.
Sorry about that, it should be fixed now.
Vid working now, looking forward to sailing reports
Tink
hi Paul, I like the fact it floats level.
so how did you figure out the hight of the akas above the ama?????
otherwise, “may the force be with you”..........
it’s got character.
I just guessed at the height of the risers, looking at it on land and guessing where the waterline would be. It is not level, it is angled down toward the outrigger end, but it does not seem to be a problem, as far as I can tell. It could have been 3” higher, or more.