Hydrofoils for opti

macca85 · #1 15-12-2009, 08:16 AM

Went to Challenge marine yesterday to grab the new horn for the nitro (if anyone needs a new horn for a nitro they are the same as the boston whaler

) and was talking about getting a few more knots out of her. Prop is at the point where if I go any more getting out of the hole will be a 20 second exercise and lifting the motor will have me chine walking like im on the piss. He suggested a hydrofoil. I've always been sceptical on these as i had one on my last boat and didnt notice much change, but he insisted that it will give the boat more speed, stability and get the boat out the hole quicker. They also have a quick release function which eliminates drilling into the outboard. What are peoples thoughts on this? anyone running a hydro on a boat doing over 45 knots and if so, what benefits if any?

Cheers

Brad Y · #2 15-12-2009, 08:43 AM

Dont even bother mate. What are your specs at the moment. Is your cav plate clear of the water? Are you getting revs within a couple of hundred rpm of the max? A hydrofoil wont give you more speed, its going to add drag.

Tell me what prop your running, what revs your doing WOT and how many holes your motor can go up. You will need to know if your cav plate is clear of the water at WOT too. Um thats about it for the moment I can start from there.

Powerbream · #3 15-12-2009, 08:53 AM

The higher the motor height the LESS chine walk. Go up as high as you can till you loose water pressure or gain revs and loose speed then drop it 5mm.

Chine walk comes with speed, just learn how to drive it and there will be no chine walk.

macca85 · #4 15-12-2009, 08:58 AM

Hey yatesy
Cav plate is out atm, still 2 holes it can go up but not sure whether its a good idea.......wont hurt trying tho. Prop is a solas 21x14. As for WOT i'm pretty sure shes right on but ive got me mate wiring it up soon to get an accurate read...nitro gauges are bin material. You know how it is, one minute its fast enough, then you want more.
The blue tub looks the goods with the new donk on her. what did you get her up to on the w/e

Brad Y · #5 15-12-2009, 09:09 AM

She did 37 knots two up, but I can trim to crazy angles so Im raising to the last hole as when i got to crazy angles she started to porpoise. Got a little work to do but i think it should go close to 40 two up by the time Im done.

How far can you trim out? is it at crazy angles or does it sit fairly level when your running. 4 blade or 3 blade prop? The guages that come with nitro are for merc engines so they should be pretty close. You want to be pulling 5500rpm trimmed out at WOT for that motor i think. If your not within 200rpm than that, then you can probably get something to fix it. What model solas are you running?

macca85 · #6 15-12-2009, 09:24 AM

Prop is a 4 blade 21x13 not 14, not sure of the model. I think graham got the prop off Chris Elliot who was running it on his nitro. Sits fairly level and can trim out a fair amount, as for the gauge maybe i need to adjust them, they are sitting too high even on idle. It looks like you can adjust them from behind but I think i'll just get smartcrafts.
How fast should 640's really go before you should just get another boat. What are peoples top speeds atm?

Brad Y · #7 15-12-2009, 09:35 AM

Seriously you wont get much unless you want to go for full hydraulic jack plate, low water pickups etc. Not really worth it in that boat. It goes fast enough FFS

Like you said if your guages are out then maybe get that done first. Basically you have the largest prop on there at the moment that suits that motor but when you get your guages done, see how high it revs at WOT trimmed out. If its 5250 or so then you can switch to a 3 blade new saturn to rev right out to 5500 and you may gain some speed. Generally 3 bladers are faster than 4's. But your holeshot wont be as good. If you want better holeshot then you go with 4 blades. Also 4 blades will grip the water better in turns and rough water and if you have raised the motor. So going back to 3 may see you blow out at hight speed at that motor height. Then you will have to drop the motor a hole, probably get more drag into the equation and get no difference.

Get your guages sorted first. And dont bother with the foil.

Brad Y · #8 15-12-2009, 09:41 AM

read this

http://www.basspro.com/webapp/wcs/st...ID=&subcatID=0

then watch this

http://s88.photobucket.com/albums/k1...gAnch=imgAnch1

Brad Y · #9 15-12-2009, 09:43 AM

Interesting to hear that chine walking is related to engine height too. Might want to get that sorted. I dont know if yours is too high or too low but do some more searching on US forums and it may help.

macca85 · #10 15-12-2009, 09:54 AM

sounds like the best thing to do for the moment....will just enjoy the new horn for now

dont think a 3 blade would be a go unless I transfer some weight up the front....170kgs of donk is a pain to get on the plane

macca85 · #11 15-12-2009, 10:08 AM

Quote:

Originally Posted by Brad Y

Interesting to hear that chine walking is related to engine height too. Might want to get that sorted. I dont know if yours is too high or too low but do some more searching on US forums and it may help.

I think I will be doing some testing on the swan this w/e...will see what that does

Powerbream · #12 15-12-2009, 11:03 AM

I dont know what sounders you have but for about 50 bucks you can get the mercury-lowrance interface cable and network the motor to your sounder. You then get digital tach and a heap of other good info.

And get a water pressure gauge before even thinking about moving the motor height or it can easily end in tears.

brad mcdonald · #13 15-12-2009, 08:22 PM

stupid question time ..... if the cav plate is clear of the water & and a hydro foil bolts on top of the cav plate ...... how is it going to create more drag when on the plane?

surely it would help push onto the plane then its out of the water and there for no more drag?

Powerbream · #14 15-12-2009, 11:00 PM

It should be out out of the water well before wot.
A hydrofoil will help holeshot and slow planing.

Shane · #15 15-12-2009, 11:14 PM

I had a foil on my motor, Honda make so it was the right one for the motor. Really good in the 8 knot zones which is why I bought it, but when I got the jacking plate I took it off. At full noise the prop wash for a fully jacked motor seemed to affect how the motor sit, actualy looked like it made the motor rock side to side. Might just be my imagination because I dont want to watch the motor when I am doing over 40 knots

But it does make your hole shot really fast, but with the jacking plate seems you can get a better angle with it trimmed down and the hole shot isnt that bad. On my fat boat that is