Doel fins/ hydrofoils

Gramas · 07 October 2012, 19:05

Do you folk have them on your rib? A lot of lads down boat yard use them on there fishing boats, just wondering if worth having them on my 90hp yam?Heard good things bout them & helping to keep bow down, if so would help aid trim?

Jim Robinson · 07 October 2012, 20:34

Fins work well if the boat is aft end heavy, ie big four stroke engine short boat which takes a long time to get onto the plane. They lift the back of the boat up getting you plaining more quickly and keep you on the plane at slower speeds.The original Dole fins were a flat wing shape. We found they got the boat on the plane well but slowed the boat down by quite a bit 5kn or so as they dragged . Recently more modern designers have come out . Attwood have a good design which are angled up so after you reach plaining speed the boat lifts and they come clear of the water so little speed loss. Attwood were supplied by Navimo - Plastlmo uk. We fitted them to Avon 560 if they had four stroke 75 -115 made a big difference.

paddlers · 07 October 2012, 20:46

Fitted my first pair on a 35hp Chrysler 30 years ago that struggled to plane without & it made a huge difference straight out with them on! Had them on my last engine an 85 Yamaha same result so I fitted the upswept style on my present 115 Mariner as a matter of course before I'd even tried it !
For me they seem to make the boats more stable & pop out quicker especially when towing a heavy waterskier (17 stone) on a ski pole & better in the turns.
To be fair for the small cost they're worth a try if you don't mind drilling four holes in your cavitation plate. The only down side is my prop cover won't go over them!!

North Shore · 07 October 2012, 20:47

I wouldn't have a Rib without an original 'Doel Fin' - beware cheap imitations. On a 90two stroke on 6.1m the difference is lower planing speed, a flat rise onto the plane and no noticeable drop in speed as measured by the chartplotter.....also makes a handy step when climbing in. More stable as well.....recommended

Courageous · 08 October 2012, 07:24

Had a whale tail on our merc for a while and it ended up "aiding" the parting of the gearbox from the mid section..... Yep the trailing edge bolt was never fitted by the previous owner and the added strain from the whale pulled the two sections apart. Nice expensive surprise....

ChristopherA · 08 October 2012, 07:37

I have fins on both ribs, a 4mt with a 40 yam and a ocean pro Zodiac with a 90 yam, plus I did fit them to a 8mt hardboat with a 130 volvo I/O that was the only one that I didn't like as when the sternwave caught you up when coming of the plane it would slew the stern round, also got the same effect when in a following sea at displacement speed.

HughN · 08 October 2012, 15:58

They are a 'Marmite' product - you either love them or you hate them. They do seem to be quite divisive on various internet fora.

I think it comes down to it being a 'one size fits all' product - its going to suit some boats better than others.

- They transformed a dell Quay Dory that my grandfather had.

- When bought with a 3.5m rib as a 'must have accessory' they were not a success: if the boat got airborne they could be one of the first things to hit the water again (and at a high angle of attack) causing the bow to slam in. On a bigger, heavier boat with this probably wouldn't be so much of a problem ('one size fits all' meant it was probably too big for that boat). They came off. Fourteen years later we still use the boat without them.

- On a hard-boat (that came fitted with them) I could never find a point where the trim that was good for the boat/engine was OK for the foils - trimming for maximum speed resulted in too much lift from the foils and not enough boat in the water. I blame them for a sudden rolling motion in swell that scared the wotsits out of me. They came off at sea then and there.

They were advertised as 'Being designed by an Aeronautical Engineer', as if this gave unlimited credibility or pseudo-mystical powers.

1) Thats wot I is and I have no credibility (or pseudo-mystical powers for that matter)!
2) If he went around sticking the same part on different aircraft without working out how each might be affected he would be an idiot.

If there is a real problem with getting on the plane and you don't mind having holes in your anti-ventilation plate they are probably worth a go.

You pays your money, you takes your choice...

Another 'Marmite' product is Smart Tabs!

tso_privat · 08 October 2012, 16:03

Quote:

Originally Posted by ChristopherA

I have fins on both ribs, a 4mt with a 40 yam and a ocean pro Zodiac with a 90 yam, plus I did fit them to a 8mt hardboat with a 130 volvo I/O that was the only one that I didn't like as when the sternwave caught you up when coming of the plane it would slew the stern round, also got the same effect when in a following sea at displacement speed.

Can you explain more about the Zodiac Pro ? Was it a 530. How did it work with 90HP. Was it 2 stroke ? Sorry for asking but I am rebuilding one at the moment and have no engine...
Cheers Thomas

longjohn · 08 October 2012, 16:07

Worked for me - recommended
http://www.rib.net/forum/f36/fins-hy...tml#post456104

9D280 · 08 October 2012, 18:08

Gramas,

Not sure from your post whether you have them or are thinking about them.

As said, they are Marmite. (other yeast based spreads are available!)

Personally, I've improved the handling, top speed & fuel economy of 2 ribs so far by removing them, but if you are "thinking", have a play with the trim of your engine and weight distribution in the boat before you start drilling the plate that wasn't really designed to be holding the back of the boat up in in the first place.....

Nasher · 08 October 2012, 18:29

Controversial I know, but I believe they treat the symptoms of a poor set up rather than improve anything in their own right.

I have used them to great effect on a Flatacraft Force 4 that I re-engined with a 55HP Suzuki triple.
The RIB was very fast, but tail heavy, and Chine walked like a Bast**d regardless of trim because too much of the boat was out of the water and it became unstable.

Putting a set of fins on the engine sorted it all out, and it was great fun to drive, but the real problem they treated was my 'stick a big engine on it' attitude and lack of understanding.

Nasher.

Gramas · 08 October 2012, 18:30

Quote:

Originally Posted by 9D280

Gramas,

Not sure from your post whether you have them or are thinking about them.

As said, they are Marmite. (other yeast based spreads are available!)

Personally, I've improved the handling, top speed & fuel economy of 2 ribs so far by removing them, but if you are "thinking", have a play with the trim of your engine and weight distribution in the boat before you start drilling the plate that wasn't really designed to be holding the back of the boat up in in the first place.....

not purchased was just researching and getting good advice, hence im posting alot being a newbie haha

ChristopherA · 08 October 2012, 19:35

Quote:

Originally Posted by tso_privat

Can you explain more about the Zodiac Pro ? Was it a 530. How did it work with 90HP. Was it 2 stroke ? Sorry for asking but I am rebuilding one at the moment and have no engine...
Cheers Thomas

The fins were already fitted when the boat was purchased second hand, it is a 2stroke engine and is used mainly for PBII courses as it has seating and we don't end up with people sitting on the tubes, it has a top speed of around 25/28 knts.

thomas · 08 October 2012, 19:46

I had them on my Valiant 450 with a Yam 50 on it, it's true, they kept the bow down and got me on the plane at lower speeds but only because the boat was poorly set up and had far too much weight at the back.

Once your on the plane, which you will be most of the time, unless you're on a river or a harbour with a speed limit, they do nothing to improve things, only cause a huge amount of drag and reduce your top speed whilst halving your MPG.

If they really were the wonder product for outboards then we'd start to see manufacturers making anti-ventilation plates bigger.

longjohn · 08 October 2012, 22:36

Surely they are only the simplified equivalent of trim tabs (common on all types of larger powerboats - are these therefore by definition badly setup/balanced to need them??) - yes they can help alleviate badly balanced or set-up boats but they can also help fine tune perfectly well set up boats. There are so many variables that can affect the balance of smallish outboard powered boats..... passenger load, fuel load, sea state, speed, power, engine weight & hull design etc etc... Engine manufacturers could not hope to provide the perfect configuration (cav plate size) for every eventuality all of the time.

It's horses for courses - may suit some set ups but not others. Either way they are are a cheap & easy way of experimenting (especially if you use the 'no-drill' ones).

clydeoutboards · 09 October 2012, 07:18

Quote:

Originally Posted by thomas

I had them on my Valiant 450 with a Yam 50 on it, it's true, they kept the bow down and got me on the plane at lower speeds but only because the boat was poorly set up and had far too much weight at the back.

Once your on the plane, which you will be most of the time, unless you're on a river or a harbour with a speed limit, they do nothing to improve things, only cause a huge amount of drag and reduce your top speed whilst halving your MPG.

If they really were the wonder product for outboards then we'd start to see manufacturers making anti-ventilation plates bigger.

sorry I 100% disagree. as stated by others on here they have there place i.e. a back end heavy boat where it struggles to get up quickly or where they would like a lower cruising speed or where the engine power is borderline for getting on the plane. so a twin engine set up on a rib, a 50hp on shetland 570 etc would be classic examples of when to use them.

Dave

thomas · 09 October 2012, 14:12

I was going on what I experienced first hand and what I was told by a RIB builder who said I'd be much better off putting ballast up front - I guess it like what was said earlier, you either love them or hate them.

Nick Hearne · 09 October 2012, 14:27

I have had them on 3 boats SR4, 5.75 Viper & a 6.5m hard boat, I found the them very stern heavy with too many people wanting to sit at the back the 6.5m hada 220hp inboard so plenty of power but you get 10 people all sitting too far back & it would really struggle to get up and go but ones fitted the fins did a great job making low spead estuary work muck better being able to trim in & putting the bow down!
I bought my SR4 with them fitted & it has a 50hp 2st so again not under powered & again I can trim in & keep the bow well down, I did try I with out the other day as it was just me going out & I gained about2 knots & it chime walked terribly without them so I put them straight back on!

The one Rib I do not need them on is my Ribeye!