tri-hull charictaristics...

[sundog]

Ive got a problem with my prop ventilating. Ive got a 1978merc115 on a 1964evinrude16'tri-hull, with a 13x17pitch prop. ventilation plate is approx 1" below lowest point on keel. prob loses water in hard hole shot, and in turns at speed. had prop cupped, and that helped some, but still ventilates in turns. everything short of swapping props seems like its where its supposed to be.<br /><br />this is my first tri-hull, and the first time Ive had this problem. it got me thinking about the tri-hulls in turns. wouldnt the outer 'sponsons' keep the boat from heeling into a turn, and cutting a clean turn? would they cause more of a 'skidding' turn that might move water over the prop differently than a monohull type boat, maybe causing tri-hulls to ventilate more often? Am I overthinking this, or what?

 

[JasonJ]

Re: tri-hull charictaristics...

You may want to work on how you are trimming your motor. My tri-hull will heel over fairly well, and I can take very hard power turns without any prop blowout whatsoever. This of course also depends on the individual boat. My boat has a large center with about 24 degrees of deadrise, so it is a bit out of the realm of the typical tri-hull. Without seeing your boat, I would guess that at the transom your boat is almost Boston Whaler-ish in that there isn't much dearise in the center section. If that is the case, it would lift the prop and cause blowout in a hard turn. Click my link below, the first pic shows the back of my boat. Is yours like that, or less in the way of deadrise? (deadrise is the measurement in degrees of the angle from center keel to outer edge at transom)

 

[sundog]

Re: tri-hull charictaristics...

Jason~ Ive looked at your pics before...very nice job on the refit. transom on the evinrude is 'boston whalerish', with very little deadrise. if you look below, scroll down to the pic that says 'easy going', and you can kind of see the transom (better pic in the 2nd link, scroll all the way down). I think your right, though...now that I look, see how low they mounted the engine in that 'easy going' pic. ventilation plate looks to be 4" below the keel. they only made these boats for about 5 years...Im begining to wonder if they had a problem with that. I was planning on lowering the engine by about an inch...now Im thinking 2 or 3. I dont care so much about drag, the boat is fast enough for me at this point (pulls my kids up on skis...what else can I ask for).<br /><br /><br /> http://www.ultimate.com/omc-boats/gallery/lit.html <br /> http://www.ultimate.com/omc-boats/gallery/sport1.html

 

[JasonJ]

Re: tri-hull charictaristics...

If it were me, I would keep the motor +- 1 inch of the keel, and investigate prop options. I am sure there is a prop that will hold better, and you can also work your trim technique. Do you have power trim? Maybe tucking in on hard turns will help hold. I had an early 60s runabout that was near flat at the transom and the prop wanted to blow out in hard turns at speed. After a trou browning spin-out I learned to either slow down for a hard turn or just not turn so hard. Good luck with it, its an interesting boat.

 

[jimmbo]

Re: tri-hull charictaristics...

These boats did appear to have a transom that wasn't quite 20 inches. I know my dads Sweet 16 had its motor mounted about 2 inches below the bottem of the transom. I didn't say keel cause the keel on this boat ends about 30 inches forward of the transom.

 

[BF]

Re: tri-hull charictaristics...

the trihull that we had in the '80's (15' excel, 60 hp johnson) also cavitated easily in corners. We just got used to the feel of just how far you could go before it would cavitate. When turning with a skier, they could cause caviation if they pulled to the outside of the corner.<br /><br />As suggested, maybe you can improve it with the prop & engine height, but I think that some trihulls just plain don't handle great. I think you hit the nail on the head, probably why they're not around so much anymore. Deeper keel ones like JJ's do look to handle better (more like a V hull). They sure don't ride as rough as our more flat bottom trihull did.

 

[Maximerc]

Re: tri-hull charictaristics...

I have owned three trihulls each acted very diffrently one was a deep V it turned the best. (heeled over) the squarer the nose the flatter the turn I did like the square nose on at high speed on flat water lots of hull lift