Hydrofoils / outboard motor fins - yay or nay

[MichaelK]

So i've been happy with my 2 x 40hp yamaha outboard motors performance.


I've been given hydrofoils or fins for my outboards and am tentative to instal them.


What are the pro's and con's to having hydrofoils on your motors?


What are your experiences with them on your motors?

[Shaun17]

Check with HappyDog… i gave him a pair that i had spare from my yammie 40's. He'll probably best be placed to tell you whether he noticed any considerable difference or not.

[MIKE PIKE]

MichaelK , i had a hydrofoil fitted to my Suzuki 40 and it did make a difference when getting the boat up and planing quicker , especially if it was loaded and tail heavy , it also allowed the boat to plane at a lower speed which means u didnt have to use lots of power/fuel and still stay on the plane , only disadvantage was it killed the top speed a bit and also created a bit more drag until it became effective , this was on flat water so not sure how it would be in the surf and rough water  , other advantage was it stopped boat porpoising and pushed the nose down a bit , ie the boat was more level and not nose high when on the plane , i took it off eventually as on a smallish boat it didnt make a huge difference unless i was really heavy loaded , best is to try them out and see if it really makes a difference under the same conditions .

[MichaelK]

Mike the reason i'm trying to get as much info as possible is because inorder to mount these fins i need to drill holes in the section of the motor that it fits onto. Which i'm loathing to do just incase i feel its hampering the boats performance.


I'd be interested to find out how they affect a boat in rough conditions like with a following sea, or if it prevents snaking on swells ect ect

[MIKE PIKE]

 Eish if its the ones u have to drill holes in the cavitation plates ..!! i had to drill mine as well and it doe'snt feel right , i blocked the holes off with a 3M product (DP490) , not cheap but sets rockhard like granite can be filed , machined drilled and sanded.  difficult decision regardless..  

[tkei]

A mate had them on his boat, not sure HP size of boat etc. He took them off as he couldnt get the nose of the boat up when necessary to go over a bit of a foamie etc. made the boat go through it he said.

[MIKE PIKE]

Yep thats the problem it lifts the stern pretty quickly when it gets up to speed and the hydrodynamics kick in and like u say going to putting the nose in to the waves headon , i'd say its more an application for really heavy boats or the skiing / watertoys guys who need to get on the plane quickly and on flattish water , also the lower hp motors benefit from it , but theres always a trade off when fitting them to the motor , adjustable" BennetTabs " are most likely the best option .

[isivuba]

Yep thats the problem it lifts the stern pretty quickly when it gets up to speed and the hydrodynamics kick in and like u say going to putting the nose in to the waves headon , i'd say its more an application for really heavy boats or the skiing / watertoys guys who need to get on the plane quickly and on flattish water , also the lower hp motors benefit from it , but theres always a trade off when fitting them to the motor , adjustable" BennetTabs " are most likely the best option .

 

[Toppie]

If I see fins/hydrofoils on a boat's engines I know immediately that the engine/s power (and weight) was not properly matched to the boat size/weight.

[Serra Moz]

If I see fins/hydrofoils on a boat's engines I know immediately that the engine/s power (and weight) was not properly matched to the boat size/weight.

Good point or debate Toppie, I was thinking more/less along the same lines. To further conversation, will the size/shape FC or CC/type of hull not make a difference as well?

[travelmember]

If I see fins/hydrofoils on a boat's engines I know immediately that the engine/s power (and weight) was not properly matched to the boat size/weight.

Not necessarily. Boats and motors are a compromise. It is very different running a light boat with minimal power at the coast and expecting the same rig to perform with 6 on board towing a skier at altitude.
Hence rather than keep 2 boats, one can make mods to the existing set up to cover more bases. One of the 27' OB boats I skipper has them and it allows much lower planing speed which is great in rough weather and it allows us to carry more weight. Likewise with the rescue duck I skipper - keeping the bow down is critical so that one can see a casualty. In most installations on the anti ventilation plate (not the floppy clip on ones) I think the benefits outweigh the negatives.


Hydraulic / electric trim tabs are a totally different issue.

[L Hooker]

I had hydrofoils attached to my 2x 50hp Mariners when they where on my 6.1m stingray duck. Why did i put them on? Simple i found the motors where a bit underpowered and put the hydrafoils on to get onto the plane quicker! They worked great on the duck and definately improved the ride. When i sold my duck i bought a 17FT TCat FC and transplanted the 50's with hydrafoils on the TCat. Tested them on the dam and all seemed good! Went down to the coast and first surf launch got the feeling that the nose was very heavy and felt like it wanted to plough through the wave and not over. Anyhow got out without incident however got the same feeling of the nose wanting to dip in between swells when running at slightly higher speeds. Beached and that afternoon whilst chatting to my oldman complaining about the feeling of the nose feeling heavy i thought perhaps its the foils, cut a long story short removed the hydrafoils that afternoon. Next day launched again and huge improvement,nose felt lighter and was not digging in. So to put it simply hydrafoils do work however depends on the boat, motor weights, your hull etc etc etc.

[MichaelK]

Thanks guys, i really appreciate the input. I think those hydofoils will just have to collect dust in my garage, i'm not going to install them

[peterblace]

2 boats here in Maputo, 31'' Yamaha cuddy, one with 115hp Yam 4stk and the other with 150hp Yam 4 stk have them mounted cause they usual travel to Santa Maria
very helpful on the low tide where certain areas are not deeper then 70cm and they need to put the boat to plane...with the hydrofoils they have the boat to plane very shorter
so in my opinion it's not a question of bad pairing (boat vs engines) but a way to make things easy for certain types of areas/navigation

[John F]

2 boats here in Maputo, 31'' Yamaha cuddy, one with 115hp Yam 4stk and the other with 150hp Yam 4 stk have them mounted cause they usual travel to Santa Maria
very helpful on the low tide where certain areas are not deeper then 70cm and they need to put the boat to plane...with the hydrofoils they have the boat to plane very shorter
so in my opinion it's not a question of bad pairing (boat vs engines) but a way to make things easy for certain types of areas/navigation

IMHO neither one of those banana boats needs hydrofoils... these boats are pretty flat as you know peterblace and they run very well with as little as 2x85 hp.

Like a lot of things boating in Maputo, I'm afraid this was another case of monkey see, monkey do!

[peterblace]

one of them does that route several times per week and noticed the difference...I'm talking about Mozaya and Number1 and they both running on 150's
4Play followed their suggestion and you can feel the difference
reason for them is to start the plane earlier on the shallow waters