Outboard hydrofoil / fins

[paintman]

Originally Posted by smallribber

4) Just take some removable ballast and put it up front (water as has been suggested in a soft container that you can fill from the sea and empty again if needed). You could even rig a small pump and battery (Kept up front) to adjust in your experimenting.

Submersible caravan water pump, the type you drop in the portable water container.
This sort of thing, you will also need a length of plastic hose:
https://www.ebay.co.uk/itm/12V-Water...t/362979985220

I use one with a small Yuasa 12v battery (sealed alarm type) for refilling my tropical fish tank.
The alarm battery I also use for powering my fishfinder on reservoir hire boats.

[Steve509926]

Or you could keep it simple and use a jug!

[Pikey Dave]

Originally Posted by Steve509926

Or you could keep it simple and use a jug!

Or a lemonade bottle. The irony[emoji849]

[smallribber]

As I said it is Just weight distribution..... Ignor all the you have got the Wrong prop brigade and lift it up an inch warriors... Just try some weight up front and it will tell you the issue then you can decide how to best overcome it...... Which might be trade up to the new Honwave T38ie. Your motor would go lovely on that baby

[Steve509926]

Originally Posted by Pikey Dave

Or a lemonade bottle. The irony[emoji849]

I resisted, it was hard, but I am proud of myself.

[Orwell boy]

Originally Posted by paintman

I did a quick google for more info on the Starfire & some reviewers said that theirs fell off in use. Attached using the grub screws.
May have been fitting error as the claims are that they fell off not long after installation.
Appears they can also be drilled & bolted.

Thanks for that little bit of joy ,if i take smallribber waterskiing in the middle of the dock i will tell him to keep his head down if he sees it coming towards him
not sure how its getting past the anode though !

[jeffstevens763@g]

Originally Posted by Steve509926

I resisted, it was hard, but I am proud of myself.

Well done mate

[paintman]

Originally Posted by Steve509926

Or you could keep it simple and use a jug!

[Limecc]

Originally Posted by Orwell boy

Thanks for that little bit of joy ,if i take smallribber waterskiing in the middle of the dock i will tell him to keep his head down if he sees it coming towards him
not sure how its getting past the anode though !

That is one UGLY looking fin
Even worse then mine (which won't fall off)

[Nos4r2]

Originally Posted by Limecc

Can you elaborate please?

Although I like the low speed effect on my hard hulled boat I would not want unpredictability at speed.

Doel fin was already fitted when I purchased it so I was thinking of trying it without when I've raised the engine two holes and fitted the four blade prop.

Random 'veering' at speed. Trim exaggerated at high degrees of trim-not just raising the bow but burying the stern too, so it felt like the stern was trying to 'pop up' when at speed in anything other than flat calm as the fins 'grabbed air and lost traction' (best way i can think of putting it).

Every boat with them on that I've driven hard has felt unsafe while being driven hard and had to back off the throttle.

[smallribber]

Originally Posted by Nos4r2

Random 'veering' at speed. Trim exaggerated at high degrees of trim-not just raising the bow but burying the stern too, so it felt like the stern was trying to 'pop up' when at speed in anything other than flat calm as the fins 'grabbed air and lost traction' (best way i can think of putting it).

Every boat with them on that I've driven hard has felt unsafe while being driven hard and had to back off the throttle.

You say fins grabbed air.......... Do you mean Prop grabbed air..

[Limecc]

My fin prevented me from trimming the prop sufficiently high to cause aeration. Stressing the tilt unit no doubt.

[Blankton]

I am still following the discussion. I have found a few measurements I made previously.

Height of transom is 15" the shaft length (s = standard or short) is 17.2". So technically I am .2" over the window recommended in that mercury marine brochure.

I used to have an evirrude which had quite long brackets. I could easily put a 1" packer under the engine and there was still a lot of bracket to grab the transom. The Yamaha has much shorter brackets, I could maybe pack it by 1/2" which would still put me 1 1/2" below the bottom of the boat, this is within the mercury marine range, but short of the dead-flush, which other people seem to recommend. To get anywhere near dead -flush I'd need to do do some structural extension to the transom.

Boat use is mainly for fishing and pleasure cruises. I don't really drive it hard in tight circles etc, my wife would moan and my fishing tackle would fall out! Things I would like to do are:

- one of the main places I use it has an 8knt speed limit. Currently I can get about 5knt displacement with a high bow and big wake, or about 11knt planing. If I could plane at 8knts that would be amazing, but maybe planing that slow is a big ask!

- Get on the plane quickly. Currently I believe it takes a long time. I have to gradually build revs (another post recommended this, I am already doing it) and try and control the bow lift. Sometimes it works, sometimes it doesn't and I have to come to a dead stop and try again.

- rougher seas. Something I try to avoid, but if trying to make way through some chop/swell, if I am negotiating some swell (not jumping straight over the top, it isn't an 8m rib!) I can easily loose too much speed and fall off the plane. Getting back on in these conditions is even more difficult.

I hope this makes sense. I felt that maybe some of the comments made previously were perhaps with large ribs in mind, where you are held into a bucket seat and going for very high performance. Really I am just plodding around compared to some of those users!

[jeffstevens763@g]

personally I've never achieved a planning speed of 8knts more 10 but even then it soon drops off in anything other that flat calm my current boat and the one before will happily plane at 11-12 knots in good conditions but 15 is more the norm in the chop when its rough i run at displacement speed any way

[Limecc]

I think 8 knots is achievable with fin. As I stated previously my 4.2m rib would plane at 10 or 12 knots (current or tide depending how low) without hydrofoil and my present 4.5m boat WITH hydrofoil rises level with the height dependent on speed and I don't feel any transition point.

Assuming weight distribution is optimal, in order I would:
1. Raise the engine as high as possible, it's far too low and causing extra drag
2. Get a tach and fit a four blade prop with a lower pitch. Four blade props add lift and the lower pitch will allow full use of available engine power
3. Fit the hydrofoil of your choice, a plastic one will not break and will return to shape if deformed by striking an object.

Edit: you could reverse 2 + 3 if on a budget, with a hydrofoil you might be able to pull maximum revs with your current prop?
Edit2: you are likely over-propped though so if you buy one with more suitable pitch make sure it's a four blade.

[jeffstevens763@g]

Originally Posted by Limecc

I think 8 knots is achievable with fin. As I stated previously my 4.2m rib would plane at 10 or 12 knots (current or tide depending how low) without hydrofoil and my present 4.5m boat WITH hydrofoil rises level with the height dependent on speed and I don't feel any transition point.

Assuming weight distribution is optimal, in order I would:
1. Raise the engine as high as possible, it's far too low and causing extra drag
2. Get a tach and fit a four blade prop with a lower pitch. Four blade props add lift and the lower pitch will allow full use of available engine power
3. Fit the hydrofoil of your choice, a plastic one will not break and will return to shape if deformed by striking an object.

Edit: you could reverse 2 + 3 if on a budget, with a hydrofoil you might be able to pull maximum revs with your current prop?
Edit2: you are likely over-propped though so if you buy one with more suitable pitch make sure it's a four blade.

you cant compare a SIB with a RIB much more drag on a SIB

[Limecc]

Originally Posted by jeffstevens763@g

you cant compare a SIB with a RIB much more drag on a SIB

True but yours and mine planing speeds respectively DO compare so strange that.

Extra drag means wasted engine power as would poor hull shape.

[Fenlander]

Blankton if you have access to the outboard be interesting to know the prop it's fitted with... by part no. or pitch stamped on it. These days and more so with 4-strokes the "standard" prop supplied can vary quite a bit.

Re foils and why I don't get on with them I've experienced odd feelings of heavy steering almost as if it's become locked and just as Nos4r2 describes a kind of veering now and again as if someone else is steering the boat against where you have the wheel/tiller. But their effect varies with every boat/setup so they are certainly worth a go as last resort.

[jeffstevens763@g]

also take into account the difference between fresh and salt water buoyancy wise i only sib in the sea but would expect to have different figures in a river [lower]

[KarlTX]

There must be something wrong with your setup. Either you got wrong prop, your motor is not running properly or your transom is overloaded... or you weight 900lbs+

I have air floor Achilles 310 and I can put 2, 170lbs adults on to plane with 8hp 2 stroke yami and keep steady 17knots during calm waters. Shoot, I wondered in to the middle of the lake during 20mph winds plus 2 - 3 foot waves and I was still able to manage plane the boat... scary stuff, I tell ya