Max HP for my 15' Caravelle

[StringBox]

I have a 1971 15' Caravelle Bow Rider Tri-Hull.<br />It currently has a 1971 60HP Johnson outboard. With a 15 pitch prop it will run about 35 MPH at WOT with me and my wife on board. The hull is rated for a max 100 HP motor. I have completely restored the hull and it is in good shape. <br />Problem is I would like a bit more speed out of the boat. Everybody on the river but the pontoon boats go by my like I'm sitting still. I would also like to have enough power to easily pull a skier or tube. I am interested in finding an older, larger motor to rebuild this winter. I have been looking around for something in the 85hp to 100hp range. I am specifically interested in an older mercury 100HP in-line 6 cyl.<br /><br />What can expect in performance and fuel usage from a larger motor? Thanks for any advice. <br /><br />Here's a recent picture of the boat.<br />

 

[skier]

Re: Max HP for my 15' Caravelle

Actually, if it were me, I would hang a 1983 - 1987 Merc 90hp on the back and hold on.<br /><br />As far as fuel usage, TrailerBoat magazine did a write up on Larsons version of my Glastron 16'. They tested it with a Johnson 90 (96/97) and I have a 79 Merc 140 (Equal to a new 115 (Give ot take)). I get better mileage than the test boat did with more power. This only works to a point where you reach y our baots hull speed. After that to get 1 mph more you would need 50+ hp. You would know when you reach that speed, cause if you try to go faster, all that happens is the motor makes more noise and burns more fuel but doesn't go any faster.<br /><br />Good luck with your choice and have a great day on the water.<br /><br />Craig

 

[Spidybot]

Re: Max HP for my 15' Caravelle

The 6-cyls sure sounds better but regarding consumption a 4-cyl would be more modest. Agree with Craig though - consumption is greatly affected by the way you use your boat. A larger motor running comfortably at mid range while cruising uses less fuel than a smaller roaring at WOT (provided both are propped right).<br /><br />Also compare motor weight as a rear sitting too low in the water when at still looks and feels weird.<br /><br />Congrats on the boat - looks good !

 

[StringBox]

Re: Max HP for my 15' Caravelle

Thanks for the advice guys. I'm not to worried<br />about the extra weight. I can sit on the transom with the boat in the water and it makes little to no difference how low the stern sits in the water. I'm 6'2" and weigh about 225lbs.<br /><br />I've seen some formulas on calculateing speed vs. Horse Power. They involve the weight of the boat (unknown, guesing maybe 1000lbs, it's a small boat and looks bigger in the pics), the hull type (tri-hull), a slide rule and the phase of the moon. Any guesses at what would give me a good 45 mph cruising speed without having to go WOT everywhere?<br /><br />If I switch to a different make motor, will I have to re-drill the motor mount holes in the transom to accomodate the new motor, or are they universal?<br />

<br /><br />Thanks

 

[Spidybot]

Re: Max HP for my 15' Caravelle

Transom mount holes are standard since years back. Anyway, I'd do a check before actually doing it. Other details & fittings are not always the same (cables and links, remote control) - in case it doesn't come with the next motor.<br /><br />Regarding what hp will give you the highest cruising speed & less stress on the motor, the answer is easy: The highest hp (100) it's rated for.<br /><br />Depending on your budget, I'd shop for a 4-cyl close the 100 hp - and even check 4-strokes. Concentrate on main brands and availability of good service/workshop in your area.