outboard hydrfoils

[riverdog]

hi all im starting to prepare for a two week trip to salcombe in june , i know its early but not been on the water for over a year due to home improvements so already looking forward to the trip . i just bought hydrofoils for my mariner 9-9 im wondering if anyome has any experience of using hydrofoils and if they make any difference my boat is a 2-9 excel.

[Paul]

Hi mate and welcome back
Martin, 9-R and Philpot are the guys to advise you and I'm sure they'll be along soon
Basically the fins will get you up on to the plane quicker with a small trade off at top end speed 1-2 knots.
Martin swears by them having made his boat more responsive but I'll leave those that are in the know to advise you best
BTW.....why are you fitting them, have you an issue with your set-up

[James]

On my Sib
Without them
[*]I suffered bad cavitation
[*]Getting on plane took a lot longer

On my Rib
Without them
[*]when going slow on rivers it felt like the back was digging in to the water

I've put my hyprofoils back on and they will be staying. I like the ease of plane, handing (turning) feels better but I do loose the odd top mph.
If I was in the sea racing trying to get top speed I'd remove them.

[riverdog]

thanks for the advice , i was hoping they would improve handling on sea i dont mind too much if i lose a bit top end . Guess ill just experiment and see whats best. Speed restrictions limit you a fair bit in Salcolmbe estuary but good fun further out to sea.

[Martin]

Helloooo

When I first starting sibbing, I felt a little uneasy with the massive amount of bow rise under power and during wind. The boat felt very unstable. Not something I was prepared to take the nipper out in.
Whilst out messing about, just myself in a 3.8 wanting to gun it left the bloody thing sky high.
(Little did I know that the weather I was learning in was pretty crap for boating. )
I stumbled across the fins on a YouTube video.. My brain cogs started whirring !!!!

Having looked around for months, I decide the stingray junior was to be my choice of hydrofoil, the reviews seemed fantastic and the explanation as to the "how and why" of hydrofoils made perfect sense.

Has it made a difference?
Hell YES !!!

I can sit right at the rear of the boat, fuel tank next to me, no weight in the front at all and from standstill I can open the throttle to max and hole shot any equivelant boat to a disturbing degree.
Handling is AWSOME, when not much weight in, however - with weight on board and a slightly wavey sea it gets a little more difficult to tiller.
My sib planes at low speed, appears to have slightly better mpg (could be down to the prop upgrade also), no porpoising effect, no bow rise, no transom splash and it planes easily at slower speeds..
I can't think for one reason why i'd ever run out on my own without them on again.
A very worth while upgrade to any sib IMO.

[Si Crowe]

IMHO, Doel Fins are worth every penny, they reduce the sern end squat, ease planing and in my case on my rib stop ALL chine riding (boat wobbles from side to side at WOT). the minor penalty of the loss of 1 or 2 knots is not worth worrying about (not at 35kts anyway).

in a small sib i can certainly see the benefits...

[James]

I fully agree with what everyone says. Mine are only a cheap pair, so imagine what a decent expensive pair do lol

[PeterM]

I'd echo the advice to date - I fitted them to my 4m RIB as it was very stern heavy as I went for a max Hp engine ....its transformed to a nice handling machine now - nice cruise now & no over scary bow rise.

Oh and I've just got 2.9 excel SIB too - only 5hp though - but I'm hoping 1 up I'll make it to planning speeds

[9-R]

To me, it's really hard to say. I read of several examples like Martins and others where it completely changed their setup for the better and then there are some, like myself, where it doesn't do as well. Even though we all are referencing just a SIB, there are still so many different shapes and sizes. As we've discussed in another topic, there are a lot of different combinations that have a vastly different outcome depending upon just the engine type vs boat manufacturer.

Some of the ones that I've seen that perform well right out of the box, have a transom that is formed into more of a V at the bottom like the Zodiac Mark Series. Mine is almost flat across and has a lot of issues as I've found with others. It is bad for hull air entrapment down the middle causing ventilation at the prop.

I had a hydrofoil like Martins but it was a bandaid to my ventilation problem because my setup is different and it didn't perform as well as his. I was able to get around okay and even had a good top speed but our hole shot and acceleration sucked. Weight distribution was critical and family was getting tired of constantly moving around depending on if we were cruising, accelerating or trying to make top speed without porpoising. I think the biggest cause was the drag of the thick plastic and the lift somehow fighting the trim of the engine. I've since made a compression / anti-ventilation plate out of aluminum, with no lifting capabilities, and the performance difference is amazing. Night and day. Great hole shot, acceleration and my family can pretty much sit where they want. My lasting problem now is that the fin is no longer lifting the engine so I have to raise it on the engine / transom to try and stop backsplash.

Sounds like you need some sort of plate on your engine to negate the ventilation issue but we need more information before we can steer you in the right direction. Are you able to trim the engine lower? How does your setup react when it's trimmed all the way in to the first hole?

[philpot]

I can confirm the advantage in getting on the plane much quicker with the fins, there may be a slight reduction in transom splash but that is down to the boat and engine set up. Each boat make and model with the engine combination can have different effects in cavitation/ ventilation and is like saying how long is a piece of string so not the subject for here, I think.

The other consideration and the one that I found to be a pain in the rear was in transporting in the car as I could not transport on it's side as the fin was bending a little and did not want to break it so the whole transport thing made me rethink the situation and I decided to remove them when going on holiday as there was enough gear to carry. On 4 stroke engines, the situation is far more critical as the engine MUST lay on a certain side and the engine block MUST be higher than the prop otherwise oil will get into the block so please bear that in mind.

Would I have them again, HELL NO, the Frib doesn't need them and it would be the last resort on any other sib if transporting in the boot of my car.

Phil