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Old 01 October 2013, 14:11   #1
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Hydrofoil fins for a 25hp evinrude on rib

Hi, i have an xpro 380 rib with a 25hp evinrude (tiller) and was wondering if hydrofoil fins would be any good?
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Old 01 October 2013, 14:47   #2
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Originally Posted by JordanB380 View Post
Hi, i have an xpro 380 rib with a 25hp evinrude (tiller) and was wondering if hydrofoil fins would be any good?
Good for what? do you have a problem?

Welcome to Ribnet BTW
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Old 01 October 2013, 14:51   #3
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Would they be benificial in any way, stability? Speed? Bow rise? Planing speed? I have limited knowledge on these.
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Old 01 October 2013, 15:03   #4
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Unless you have a specific problem e.g. stern heavy/bow up I wouldn't bother. Even then there are better solutions e.g. moving weight around, trim etc. I've never been convinced with fins/hydrofoils. Just IMHO of course.
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Old 01 October 2013, 15:10   #5
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Well my problem is when towing a ringo, the engine has plenty of power to do it as it did on my old boat (4m sib) but it seems to stick badly in the holeand not plane until you move everything and everyone to the front and then it planes, would the fins help this or is there something else?
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Old 01 October 2013, 15:15   #6
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Fins *might* help (at the expense of a bit of top end speed.) Trimming way in will help. Lightening the load will help. You already found out that balance helps.

jky
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Old 01 October 2013, 15:17   #7
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Quote:
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Would they be benificial in any way, stability? Speed? Bow rise? Planing speed? I have limited knowledge on these.
I have used them on my 4m rib with a 30hp yam with no power tilt
they reduce overall speed due to drag
on my rib they lower my planing speed, useful for me on windermere where there is a speed limit.
on my boat they reduce bow rise, and the boat rises on to the plane quicker.

as others have said they have many disadvantages, I don't use them all the time
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Old 01 October 2013, 15:20   #8
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I'd say a 25hp is probably on its limit with a 3.8m rib & towing a ringo. What prop do you have on it & are you getting max RPM at WOT? You should be somewhere around 5500rpm
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Old 01 October 2013, 15:33   #9
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I have a 10X13 stainless prop and i do get max rpm at WOT, was thinking weather a 10X15 may be better?
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Old 01 October 2013, 15:37   #10
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Quote:
Originally Posted by xs 400 View Post

I have used them on my 4m rib with a 30hp yam with no power tilt
they reduce overall speed due to drag
on my rib they lower my planing speed, useful for me on windermere where there is a speed limit.
on my boat they reduce bow rise, and the boat rises on to the plane quicker.

as others have said they have many disadvantages, I don't use them all the time
I go out of Saundersfoot, south wales and there is 10 knot speed limit for a km and then no limit, not to bothered about top speed just the bow rise and planing speed, so they seem to work for you.
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Old 01 October 2013, 15:40   #11
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Fins worked for me. As xs400..not worried about max speed, sorted excessive bow lift and plane speed dropped to an acceptable 12ish knots.

With power trim ....no negatives for me except loss of a couple of knots off top end speed.
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Old 01 October 2013, 15:42   #12
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Fins worked for me. As xs400..not worried about max speed, sorted excessive bow lift and plane speed dropped to an acceptable 12ish knots.

With power trim ....no negatives for me except loss of a couple of knots off top end speed.
I have a tiller engine without power trim so would it have the same results ?
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Old 01 October 2013, 15:45   #13
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I have a tiller engine without power trim so would it have the same results ?
Possible, but you may have to accept more of a compromise..and manually change trim settings more often. Maybe find a set of clip on fins?
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Old 01 October 2013, 15:46   #14
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Originally Posted by JordanB380 View Post
I have a 10X13 stainless prop and i do get max rpm at WOT, was thinking weather a 10X15 may be better?
Going up in pitch isn't going to help, it'll make your holeshot even worse. An 11" might be the way to go.
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Old 01 October 2013, 15:47   #15
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Going up in pitch isn't going to help, it'll make your holeshot even worse. An 11" might be the way to go.
Thanks so you suggest an 11" prop over fins?
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Old 01 October 2013, 16:06   #16
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Thanks so you suggest an 11" prop over fins?
It would be my choice, maybe not the right one, but it's the way I'd go. That's after trying all the no cost options, make sure the engine is at the correct height & trimmed. Move some weight around, shift it forward, generally play around & experiment. Where is the towrope for the ringo attached to the boat, is it high on an "A" frame, or low down? Propping is a black art, a lot of trial & error is involved.
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Old 01 October 2013, 16:13   #17
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It would be my choice, maybe not the right one, but it's the way I'd go. That's after trying all the no cost options, make sure the engine is at the correct height & trimmed. Move some weight around, shift it forward, generally play around & experiment. Where is the towrope for the ringo attached to the boat, is it high on an "A" frame, or low down? Propping is a black art, a lot of trial & error is involved.
The towrope is on the transom, maybe ill just have to invest some money and have a play and see whats best, thanks for the help anyway
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Old 01 October 2013, 16:17   #18
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The towrope is on the transom, maybe ill just have to invest some money and have a play and see whats best, thanks for the help anyway
You're welcome, sorry I can't be more conclusive, but as I said, it's a black art. Try & borrow different props rather than buying, swapping them over is easy enough.
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Old 01 October 2013, 17:03   #19
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Originally Posted by JordanB380 View Post
Hi, i have an xpro 380 rib with a 25hp evinrude (tiller) and was wondering if hydrofoil fins would be any good?
I had very similar set up (3.8m Valiant + 25hp two smoke manual trim) although weight further forward as we had console, Hydrofoils worked for me they made a huge difference when towing ringo's and wakeboarding far easier onto the plane and would plane at lower speeds (only ever pull teenagers/small adults it would struggle regardless with anyone over about 12 stone)
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Old 01 October 2013, 17:12   #20
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I had very similar set up (3.8m Valiant + 25hp two smoke manual trim) although weight further forward as we had console, Hydrofoils worked for me they made a huge difference when towing ringo's and wakeboarding far easier onto the plane and would plane at lower speeds (only ever pull teenagers/small adults it would struggle regardless with anyone over about 12 stone)
That's exactly what i want, ill invest in some fins as they are only 20, thanks for the response
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