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Old 19 July 2015, 06:21   #21
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I removed a set from a motor I purchased and had capitation issues - turned out the drill holes in the anti cavitation plate (these were the older style Doelfins that required drilling) were venting air directly above the prop allowing it to slip wildly at lower speeds - I taped the holes up with gaffer tape as a test and the slipping vanished. So lesson learnt for me - if you remove a set or see holes left from when a previous owner had a set make sure you plug them with a decent epoxy metal filler.
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Old 19 July 2015, 07:45   #22
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Given that the involve drilling holes in the anti ventilation plate no manufacturer is going to warrant them. I've never seen any official guidance from a manufacturer suggesting bearing issues, have you? Can you share it with us?

If they were universally great then manufacturers would offer different leg designs with bigger plates built in. That they don't tells me that they arent needed by a big part of the market.
Im going by what new outboard dealers have told me, Ive bought 4 new engines in the last 5 years. We get 5 year warranties (on most brands) and have the weather where people tend to put hundreds of hours per year on there outboards which may be the reason manufacturers tell us not to fit them. My rib Ive only owned for a couple of months is just having its 100hr service this week and this is mid winter when I dont use my boats as much (its also one of 2 boats I own which both log around 300hrs per year).

As we've seen with many things on here things are much different in regards to regulations etc, it seems a little silly for me to contact manufacturers in the UK to ask if they warranty outboards with fins fitted. As for here you will be told by any new outboard sales person.

Over here we have a much larger boating community than the UK even though the population is much smaller

Maybe over there manufacturers have no problems honouring the 5 year warranty, why not ask.

Jon
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Old 19 July 2015, 09:41   #23
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Jonp, I'm not seeking a warranty on an engine (with or without Fins) so it would be bizarre to go and ask. As a general rule though I discount anything told to me by sales people either promising that something is or isn't covered / required. Now if the engineering department produced a document (although how they would know with dubrus' no drill ones I'm not sure). I'm not doubting they will refuse a warranty claim, I am just wondering if there is real basis to YOUR claim that fins exert undue wear on the mounting hardware.

Im surprised it's much of a new engine issue, since presumably new engines give you the chance to correctly spec the engine first time. Fins tend to be a solution to a compromise.

Since Dave has a used engine with probably no warranty it's all a little academic unless there is real evidence they harm the engine.
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Old 19 July 2015, 15:23   #24
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I personally don't like them and hate to see holes in a leg where they have been fitted.

But that said I fitted some to a 3 m rib with 15hp that wouldn't plane 4 up and does now so they do have their use

I would only want to fit any in extreme cases though.

For the sake of 25 i would fit some and try it. What doesn't work for someone might work well for you
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Old 19 July 2015, 18:10   #25
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Jonp, I'm not seeking a warranty on an engine (with or without Fins) so it would be bizarre to go and ask. As a general rule though I discount anything told to me by sales people either promising that something is or isn't covered / required. Now if the engineering department produced a document (although how they would know with dubrus' no drill ones I'm not sure). I'm not doubting they will refuse a warranty claim, I am just wondering if there is real basis to YOUR claim that fins exert undue wear on the mounting hardware.

Im surprised it's much of a new engine issue, since presumably new engines give you the chance to correctly spec the engine first time. Fins tend to be a solution to a compromise.

Since Dave has a used engine with probably no warranty it's all a little academic unless there is real evidence they harm the engine.



As I said right at the beginning the handling issues Ive had in fibre glass hulls wouldn't happen with a rib, a rib wont let you bury one side of the boat in side swell.

Checked both my Suzuki and Yamaha warranty books and both have a disclaimer that anything fitted to the engine which is not standard can void the warranty (this also includes the wrong pitch prop).

The bennett tabs Ive fitted to 3 of my boats all improved performance greatly across the board. Being able to put more pressure to one side of a glass boat (what Ive used them on) and stop proposing etc were a quick easy fix, they also made the boats feel like much bigger boats in rough sea handling.

With an engine that doesn't have electric trim I would be very cautious of what I put on it, at least the Bennett's have 3 different pressure settings. If the foil brings the nose of the boat down to much your only choice is to take it off and fill the holes. My rib handles badly with to much nose down trim.
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Old 19 July 2015, 18:31   #26
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... and stop proposing etc...
Certainly many a person here will suggest that proposing ruined the enjoyment of their boating!
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Old 19 July 2015, 18:51   #27
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As an alternative to fins why not temporarily block the flooding hull & see if that helps with your youngster it might be your just not going fast enough to dump the hull & hence the nose up attitude
I've used Doel fins to good effect but they do seem to be a marmite thing
Can't imagine any damage to the engine other than a couple of extra holes though so for 25 quid probably worth a go
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Old 19 July 2015, 19:02   #28
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I have the Stingray Junior fitted to my Suzuki, Its made a hell of a difference to my sib.
It planes straighter, at lower speeds, very little bow rise on hole shot..
A remarkable improvement, and with the solas stainless added at the same time, Oh Yes!!!!
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Old 20 July 2015, 05:16   #29
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as for warranties and such i cannot comment,

but on a personal note over the years i've had a few small (sub 5m) boats from...

a flatacraft force 3 (not the gt) with a 9.9hp on the back, doelfins fitted after not wanting to plane with 3 people. fitted em, planed well and solo cavitated far less in tight turns.

avon SR4 with old classic 50 merc (45hp) again with and with out the boat performed better with the fins, pulled skier out well and cruised at lower revs for far longer,

fletcher arrowflyte 14 with 75hp 2 stroke no doelfins fitted. had PT&T so was easy to trim out and never needed them.

now have avon supersport s3.45 with 40hp 2 stroke, without doelfins was very skittish regardless of trim (manual) so fitted some fins, now is planted and stable, the arse lifts better getting on to the plane.

for me (and this is just my opinion) smaller boats and smaller engines without PT&T do benefit from the fins. the manual tilt can only do so much and weight distribution is even more important. even more so for equivalent 4 stroke engines which weigh 20% more on the transom, the extra lift proved cannot be a bad thing.

the proof is in the pudding and an SR4 that wouldn't pull up a monoskier (me at 20 when i was skinny) without the fins to being able to with them with no other adjustments speaks volumes. you may loose a knot or two at the top but that's no biggie in reality cos nobody pins the throttle 100% of the time. real world cruising and comfort mean more (to me)


as for manufacturers not fitting fins as standard, how are they to know what application the engine will be employed or what boat they will be bolted on. they simply try to the best they can for the majority of usage.
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Old 20 July 2015, 06:51   #30
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oh, additionally i bought these ones...

HYDROFOIL STABILISER FINS FOR 4-50HP OUTBOARD ENGINE, FISHING, RIB, BOAT | eBay

they are angled up a few degrees so follow the V of the hull better and are quite small unlike the standard doelfins. these are rated up to 50hp.



not the best photo but you get the idea and bolted on as far back on the cavitation plate as possible so the rear edges of the fins are level with the aft edge of the cav plate.
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