Hydrofoil

ajstars · 12 November 2016, 21:26

I had a hydrofoil on my old Yamaha and it made a huge difference so I am thinking of fitting one to the Honda 225 to get it on the plane quicker.
I have noticed that it currently leaves a fair amount of wash compared to some others too.
Was looking at the Stingray Starfire, what are thoughts on here?

beerbelly · 13 November 2016, 07:26

my thought is maybe your Yamaha wasn't set up right in the first place if a fin made such a huge difference .my osprey came with fins fitted to the outboard when I took it out it didn't feel particularly quick for a having a 130hp outboard and was producing quite an impressive rooster tail .so we removed the fins and raised the outboard so the cav plate was level with the keel (it was an inch and a half lower) now there's no such watery display and the whole thing just feels a lot better and we have gained a couple of knots. them fins might be ok to cover up other issues without really fixing them

ajstars · 13 November 2016, 08:52

That was my thoughts too, I have no experience of setting up an outboard so may have to play around a bit. It's a heavy lump though at 3/4 tonne to lift!

beerbelly · 13 November 2016, 09:00

my 130 yam was too heavy for me to lift but with a trolley jack and a block of wood under the bottom of the transom mounting part of the outboard. a ratchet strap around the powerhead to the a frame. fine tuning using the jockey wheel and only removing the fixed hole bolts and just slackening the slide mount bolts I did it on my own

willk · 13 November 2016, 09:16

If the Honda is set up correctly, it should have no problem popping a 7+m RIB onto the plane quickly. The Honda doesn't weigh 3/4 of a ton, BTW

Before you go to any extreme lengths, consider the loading on the boat - a lot of weight in the stern is hard work for any engine to overcome. Also examine the position of the engine when it is fully trimmed in/down. Is there something preventing the leg coming fully down?

I'm instinctively repelled by the idea of hydrofoils/doel fins. Sure, they provide lift, but they do it through the fin plates on the engine which can't have been engineered for the ongoing stresses? They continue to exert forces on the engine even when you're up on the plane, or turning hard which must effect the general handling/performance of the boat.

ajstars · 13 November 2016, 09:45

I think what it needs then is a bit of work setting it up. Probably doesn't help that the throttle is currently set up badly with a very small range of movement at the top end which controls everything.

Last Tango · 13 November 2016, 14:33

Quote:

Originally Posted by willk

I'm instinctively repelled by the idea of hydrofoils/doel fins. Sure, they provide lift, but they do it through the fin plates on the engine which can't have been engineered for the ongoing stresses? They continue to exert forces on the engine even when you're up on the plane, or turning hard which must effect the general handling/performance of the boat.

In reality they are never going to produce more lift than the weight of the engine it's self so, if anything, they are reducing the strain on the engine mountings. As you say, they are transmitting that "lift" via the anti-ventilation plate but I haven't heard of any failures as a consequence. ("Chip in" anyone who has).
I've fitted them to several boats in the past. They do help keep a boat on the plane at lower speeds, can help get an underpowered one onto the plane and when setup right doel fins ride above the water so have no effect on handling whatsoever.
Having said all that, I agree, fins or hydrofoils aren't the solution the OP's problems. Plenty of power.....just needs set up right.

Last Tango · 13 November 2016, 15:44

Sorry "at speed, ride above the water" (to late to edit)

Nos4r2 · 13 November 2016, 17:48

So far, every boat I've helmed that wasn't massively underpowered and had doelfins/hydrofoils on has had some pretty scary handling issues at WOT when trimming up.

Last Tango · 13 November 2016, 18:43

Quote:

Originally Posted by Nos4r2

So far, every boat I've helmed that wasn't massively underpowered and had doelfins/hydrofoils on has had some pretty scary handling issues at WOT when trimming up.

I suspect the issue with the handling was down to more than the Doel fins.
Maybe you're idea of "massively underpowered" is different to mine. My 18 ft Searay would do 50mph WOT, had fins so as I could get it out the hole four-up with a 23" prop and besides that benefit, they made absolutely no difference to the handling what-so-ever. They aren't touching the water at that speed unless the engine is set to low. Similarly my Seapro 520 had them on the 75hp merc that would do about 43mph WOT. again no issues, they are completely clear of the water at that speed. I've never ventured into the 60/70mph + range where I guess there might be some aerodynamic effect but certainly nothing untoward at 40/50 mph.

ajstars · 28 November 2016, 13:58

Going back to the original thread, the engine is set to lowest position and the fin plate sits around two inches above the bottom of the boat. It could be that it was not fully trimming down before but I have serviced the tilt since then.

jyasaki · 28 November 2016, 15:34

Personally, for that big a boat, I'd look at trim tabs before a hydrofoil. I think they're a more direct approach at reaching the desired solution. Tougher to do on a small boat with limited transom area, but should be fairly easy on a bigger hull.

jky

Pikey Dave · 28 November 2016, 16:08

Quote:

Originally Posted by ajstars

Going back to the original thread, the engine is set to lowest position and the fin plate sits around two inches above the bottom of the boat. It could be that it was not fully trimming down before but I have serviced the tilt since then.

That doesn't sound right to me. Engine at lowest setting & AV plate 2" above keel. Sounds like it's the wrong length shaft for the boat. Does it cavitate easily?

ajstars · 28 November 2016, 16:41

It does cavitate fairly easily I guess. I will see if I have any pictures

ajstars · 28 November 2016, 16:42

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Not the best photos but all I have

ajstars · 28 November 2016, 16:44

ajstars · 28 November 2016, 16:44

The engine is not in fully lowered position in these photos

Pikey Dave · 28 November 2016, 16:51

Difficult to tell from the photos, in one photo the AV plate looks lower than the keel & higher in the others. When you say "fin" plate, which plate are you referring to? The AV plate is the largest plate at the lowest point, directly above the prop. This should be slightly higher that the keel with the engine trimmed down so that the plate & keel are parallel

jeffstevens763@g · 28 November 2016, 16:58

Last pic looks like the cav plate is 50 MM+ below the keel and the engine is on the very top bolt hole so can only come up.
Also looks like second hole has been used at sometime with a washer ring mark on it

ajstars · 28 November 2016, 17:05

Ok, I will go and play with it and drop it down to see exactly where it sits.
In relation to the trim tabs, I have seen electric and automatic ones. I will be honest in that having never seen them in action I don't understand how they work. I guess they keep the water down at the back rather than allowing it to rise and hence give lift as well?