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Old 07 April 2008, 10:46   #1
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Country: UK - England
Make: very little ribtec
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Doel Fins or Lifters??

Has anybody any experience comparing Doel Fins and large trim tabs like Lifters (from Maxi-Marine)? I've now got my little 2.9m Ribtec tender and 15hp two-stroke outboard and am very impressed with its performance, but it does seem to be all or nothing. To get on the plane you've got to open the throttle almost wide open, then it accelerates like mad and goes very well. Two up it will plane, three up it really struggles, as the bow rise is massive and its pushing a huge wave of water.
I have the rib on an inland waterway where there's a speed limit of 10kts but going flat out draws attention to yourself and is likely to get you fined. I'd like to be able to plane below this speed if at all possible on a reduced throttle, and think that either hydrofoils or the lifters are the way forward, especially as they should help improve load carrying ability.

I'd be happy with either solution, think i'd prefer the fins as you don't have to mess around removing them for the wheels to go down, but if the lifters would perform better then I'd fit those.
I'd really like to try both out, but don't fancy drilling holes in the cavitation plate and the transom, only to have to fix one set of them later!!

Any thoughts please??
thanks, NIck.
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Old 07 April 2008, 15:30   #2
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a few years ago i had two smaller ribs one with 25 hpfitted tabs on the cavitation plates made a huge diference in poping the rib up onto the plane i would recomend this is the way to go
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Old 07 April 2008, 18:07   #3
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Try a tiller extension to bring the CG forward when getting on the plane. My mates similar sized boat would plane 2 up with a 6hp. Just.
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Old 07 April 2008, 18:38   #4
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Iam about to give some smart tabs a try . I have searched lots for results for them and not really seen any negatives , look out here they come
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Old 08 April 2008, 08:17   #5
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Peter, I take it you mean fins rather than tabs? Tabs mount on the transom, fins on the outboard... Thanks for the recommendation anyway.

Ian, you seem to have decided that smart tabs are the way to go. Are you fitting them on your main rib or a smaller one? There seems to be a consensus that on larger boats the trim tabs are a better bet than hydrofoils.
Hydrofoils do seem popular on smaller outboards though.

As holes in glassfibre are much easier to fix than holes in the cavitation plate of an outboard though I think I might try the lifters first and see how I get on.

Just a pity that you can't get a decent clamp-on hydrofoil so that you don't have to drill holes in the outboard. Or can you???

Nick
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Old 08 April 2008, 10:40   #6
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I have fitted them to my last two boats & they work very well & are a cheap alternative to trim tabs!
I have them on my alpha 1 drive with a 4.3Lt 220 hp & B4 I fitted them going under plaining speed the bow would be up in the sky, also with say 10 people on board all sitting around the stern it was one hell of a job to get it on the plain! (I know I could ask them to move forward)
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Old 08 April 2008, 16:56   #7
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Quote:
Originally Posted by nickd View Post
Peter, I take it you mean fins rather than tabs? Tabs mount on the transom, fins on the outboard... Thanks for the recommendation anyway.

Ian, you seem to have decided that smart tabs are the way to go. Are you fitting them on your main rib or a smaller one? There seems to be a consensus that on larger boats the trim tabs are a better bet than hydrofoils.
Hydrofoils do seem popular on smaller outboards though.

As holes in glassfibre are much easier to fix than holes in the cavitation plate of an outboard though I think I might try the lifters first and see how I get on.

Just a pity that you can't get a decent clamp-on hydrofoil so that you don't have to drill holes in the outboard. Or can you???

Nick
yes I have fitted them to my main boat but have yet to try them out , its not a rib , but that makes no difference for this topic .
Take a look at smart tabs website , I know its thier own advertising but it does give a good comparison between a doel fin and a trim tab .
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Old 08 April 2008, 17:31   #8
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Thanks ian, I'll have a look. The more I look at it the more I think that the lifters are the way to go. It would be nice to do some comparitive testing, but getting any meaningful results must be dificult otherwise you'd have thought the manufacturers would already have done it for their advertising literature.
Nick
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Old 09 April 2008, 07:01   #9
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I've had Doel Fins on a 4.7 Avon for years. They work well and as I've posted before, allow a very convenient platform to use when re-boarding the boat, from the water. We spend a lot of time in the water here which may not be such a pressing issue where there are ice cubes floating around the boat!
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Old 10 April 2008, 06:41   #10
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Personally, I've removed doel fins from two boats I bought second hand. The drag took 2 & 4 knots off the top speed, and I didn't like the handling. Also drilling to fit them will kill the paint / corrosion warranty if it's new. Mind you if the speed limit is 10 Knots it may be the way to go as Vmax will be irrelevant.

Have you tried playing with the engine trim? You may be a hole or two too far out. Alternatively if you regularly have that number aboard and need to plane slower, try a slightly lower pitch prop.

As Matt says, a tiller extension might be the best bet - thing with boats as small & light as that is you & your crew are a probably a good 2/3 of the weight of the setup, so your positioning will be crucial. I've regularly used an "OMC Express 2.8" with an 8Hp. if you just sit there at the stern it takes forever to plane and behaves exactly as you describe. Move forward to get over the hump and move back once planing it goes like stink! If you have a crew, use them as mobile ballast!
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