Trim tabs for a 11' RIB?

[nathan007]

Hello!

I run a 11' RIB which is pretty heavy at 220lbs, coupled with a 15hp yamaha 4 stroke.

I find it "long" to get on a plane, and must keep a good speed before falling off it. Even with weight repartition. If i carry passengers it's even worse. It will barely plane with 3 adults but i need to keep it WOT which i do not like.

I tried a hydrofoil, it helped a bit, but the best improvement have been a 4 blade prop, but its still not good enough for my taste. I was thinking about trying a set of Maxi Marine trim tabs, they look like they would kick ass, still i need to make sure i can run the motor trimmed when in shallow waters without hitting them..

Anybody tried them? A similar upgrade?

I tought of getting a 25hp yam, but the 4 stroke will be way overweight for the rib, and i'm not ready to dish out 4000$ just to go faster/faster

Thanks!

[mayday12]

if you are referring to the "lift mates" - the plastic tabs that mount to the end of the transom - then i swear by them! they fill in the space between the tube ends, and effectively add waterline length. the dingy will plane with less hp, stay on plane longer, and doesn't fall off (no backwash when slowing). ive gone through 2 sets over the years and wouldn't ever go without. very satisfied customer
edit - to answer your other question, they don't interfere with the motor tilting - you do have to be careful if running in shallow mode and turn sharply - the prop can then hit the side of the tab

[seahag]

I had a similar problem once that was greatly solved by installing a plastic fin on the lower unit. I think it was called a "dol-fin" or something like that and maybe $25 then? Put the boat right up on plane, had no adverse effects, and I think it helped stabilize from porpoising too. For the money you couldn't go wrong to find a quick and easy solution, and for sure it will help, not hurt.

[seahag]

https://www.googleadservices.com/pag...Qwg8IJA&adurl=

Hopefully this works, I've never tried to post a link. Anyway, googled it and it is called "doel-fin" and this one was on eBay for $33

[svHyLyte]

You might want to look at the Stingray Stinger as an alternative to trim tabs or doelfins. They are quite effective.

[hobopacket]

Same as a hydro foil which he has tried.

I would try lift mates.

Or go for the good ole 25hp 2 stroke. Almost same weight as your 15 4s

[Dockhead]

Originally Posted by hobopacket

Same as a hydro foil which he has tried.

I would try lift mates.

Or go for the good ole 25hp 2 stroke. Almost same weight as your 15 4s

I'm not surprised you are having trouble planing -- 15hp is not quite enough.

I had a similar RIB (Avon 340), a bit heavier with center console and wheel steering. I had a 25 hp two stroke Mariner.

It needed all its power to plane with four people.

I added the fins to the engine leg, and that helped a lot, but I still can't see planing with more than two or three people on board, with 15 hp.

I would go with the light weight 25 hp, if easy planing is important to you.

There are some new four strokes (Suzuki?) which are apparently almost as light as the old two strokes.


I went the other way, got rid of the heavy dinghy, bought a lighter Avon 310 Lite RIB with only 8 hp. I will plane with two people, but only with difficulty with three, and not if they are large people. But I don't really need this all that much -- 90% of my dinghy use is puttering around at four or five knots.


The Suzuki 20 hp four stroke only weighs 97 pounds, so less than my 25 hp two stroke did. Might be a good choice.

[Cheechako]

15 HP marginal for that heavy RIB with 3 adults. Double floor? I think some 20HP aren't much more weight. If you are planing that RIB with 3 adults you are doing pretty good. I always found , with a load, that getting my heavy (135#x15HP) RIB on plane was easier by shifting weight forward at just the right moment.

[DotDun]

I have a lightweight 340 aluminum rib (double floor) with Suzuki 20hp 4-stroke. It comes right up and planes in less than 2 boat lengths with 3 adults. Haven't had 4 in it yet. Boat is 134lbs, engine 106lbs (incl. electric start), small battery, 3 gals fuel tank, and anchor. It easily redlines with 3 adults, hence I believe it'll plane with 4.

I had a 15hp Mercury 2-stroke (78lbs) on a lightweight 310 rib (105lbs boat). It would plane with 3 adults but not 4.

[nathan007]

Thanks all for your helpful replies!!

I installed the Stingray hydrofoil, it helped but its' not quite enough. Yes, the RIB i got has a double floor. Originally we had a 10' with foldable plywood floor, that thing would go so fast, but i use it on Lake Champlain, and wanted something that felt solid.
Of course the best alternative would be a nicer, more powerful engine, but money is an issue at the moment. I will try the lifters see if they help, they seem affordable and i've been reading some good reviews. 75% of use with this RIB is me riding solo (200lb), occasionally my brother is there and it bogs down (he's + size hehe), if not the 25% is traveling from the boat to shore (with 2-3passengers + gear) where speed is rarely an issue.

When i will blow the engine, i may feel slightly happy :P

[Cheechako]

Originally Posted by nathan007

Thanks all for your helpful replies!!

I installed the Stingray hydrofoil, it helped but its' not quite enough. Yes, the RIB i got has a double floor. Originally we had a 10' with foldable plywood floor, that thing would go so fast, but i use it on Lake Champlain, and wanted something that felt solid.
Of course the best alternative would be a nicer, more powerful engine, but money is an issue at the moment. I will try the lifters see if they help, they seem affordable and i've been reading some good reviews. 75% of use with this RIB is me riding solo (200lb), occasionally my brother is there and it bogs down (he's + size hehe), if not the 25% is traveling from the boat to shore (with 2-3passengers + gear) where speed is rarely an issue.

When i will blow the engine, i may feel slightly happy :P

BTW, have you tried adjusting the engine angle in the engine bracket? That can help getting up on plane...

[nathan007]

Originally Posted by Cheechako

BTW, have you tried adjusting the engine angle in the engine bracket? That can help getting up on plane...

It was the first thing I tried, then I changed propeller twice (ended up with 4 blade solas with one pitch less, it really helped, not the same engine anymore), then added stingray hydrofoil, which also helped getting on a plane quicker.. I'll try lifter/tabs this season, if its not enough, I'll shop for a bigger engine, hoping I'll be scared for my life when I WOT hehe

[a64pilot]

Trim tabs will not be as effective as moving the weight forward, they try to accomplish the same thing as do those fins by lifting the stern, but that adds drag, most efficient thing is to move weight forward, if that doesn't do the trick, then I'm afraid you may just not have enough thrust.
You may want to make sure your motor isn't too deep, that wide plate above the prop is called the anti-cavitation plate, and it should be right at water level when on plane, if it's completely under water, then the motor is deeper than optimum and that increases drag

[nathan007]

When spring comes I will make sure the engine depth is right. As for moving weight forward, I installed the fuel tank in front, and try my best to be in the middle for best distribution.

[mayday12]

Originally Posted by a64pilot

Trim tabs will not be as effective as moving the weight forward, they try to accomplish the same thing as do those fins by lifting the stern, but that adds drag, most efficient thing is to move weight forward, if that doesn't do the trick, then I'm afraid you may just not have enough thrust.
You may want to make sure your motor isn't too deep, that wide plate above the prop is called the anti-cavitation plate, and it should be right at water level when on plane, if it's completely under water, then the motor is deeper than optimum and that increases drag

Actually, that's not true - and I'm speaking from personal experience - i.e I DO have the trim tabs - what they do is "fill in" the aft end of the dingy, between the tube ends (and they are flush with the transom, so not any extra drag) - and since we know planing ability is related to waterline length (for the most part) it allows planing with less horsepower. It's also why they are way more effective than those little "wings" that fit to the motor.