Hi people, I trust every one had a great easter break. My problem, apart from life, is bouyancy. I dont no if you have seen "princess" in the projects but she is a 23'cedar planked hull with an 8'2'' beam and 12 degree dead rise, weight fully loaded aprox 4500lb. we have installed a 165 hp turbo diesel instead of the 350 small block chevy that she originally had and the weight of the diesel and leg is aproxx 490kg around the same as the oridginal chev and leg.the problem is she wants to drag her bum in the water all the time. even up on the plane with the leg trimed in she wants to ride with the bow high. if i use the trim tabs to bring her down a bit it just acts as a hand break and washes off speed. My thoughts are this,would extentions on each side of the hull at the transom help.ie carry the water line aft and use them as bouyancy tanks come boarding platform, if so what would be the sugestion for length volume etc to hopefully get her to plane a bit better. i have absolutely no knowledge at all in this area so any advice at all would be appreciated
cheers john
One issue you might have is weight distribution. Even though the motors you swapped out may weigh about the same, their weights are probably not distributed the same. Perhaps try and move some weight forward...battery....fuel tanks if they're not intergrated into the hull...any bait/live wells...coolers....etc. If the prop is sitting any lower in the water than the original configuration, that will have an effect too. Prop pitch will also have an effect.
ReplyDeleteJem, have done that, i only use the foward fuel tanks which are under the bunks in front cabin,120 ltrs each, both batteries are under sole at helm footrest, the only weight aft is the engine assy, the problem i think is this hull was designed to have engine amidship with shaft drive and is just a little to short for stern drive , not sure only guessing. john
ReplyDeleteGreetings John - Just reading your query and wondered if perhaps the problem with center of balance shift re your engine swap is less of bouyancy than change of shaft horsepower and propeller bite due to wheel size/pitch for that new power curve (shaft horsepower). Strangely enough I believe prop settings have a great deal to do with the shifting of center of balance as well as center of effort. If you can lay your hands on a copy of Ian Nicholson's Boat Data Book (see the review here at the site), there are some really nifty instructions about how to make measurements and equations to graph out what you need in the screw department. Gee that sounds nasty....lol. But it sounds like a good and cheap avenue to check out before you start pumping helium into some small locker on her. If you can't lay your hands on said tome, let me know and I'll stuff and get them to you. (Definitely cheaper that way.lol) Cheers, PS1
ReplyDeleteThat last sentence should have said; If you can't lay your hands on said tome, let me know and I'll scan stuff and get them to you. (Definitely cheaper that way.lol) Cheers, PS1
ReplyDeleteP.S.1 hi and thanks for the interest, I'm sure I''m not alone in experienceing these problems with a repower. I'm running a 290 volvo duo prop leg running A2 props which gives me a w.o.t of 3900 rpm just over the the 3600 rpm max hp figure. I have thought of changing props but at $1200 a pair for new, and no one will loan me a set to try before i buy its a risk i can't afford. I shore would like to see the data you have if its not to much bother, appreciate your time and concern cheers john
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