BOAT SPEED

[youri_bujko]

I have a Zodiac Pro 550 with a 115 Hp Tohatsu engine. I just installed a Stingray Hydrofoil on my engine. I had to change the pitch of my prop. from 19" to 15" to keep max RPM at 5500. My boat rides very well, but I feel that I sacrificed a lot of top end speed. My top speed is now 30 knots. Is it normal? Anybody with a similar experience?
PS: that is with a full gas tank (40 gal), some gear and myself (220 lb); also the new prop is a 3 blade composite prop from Piranha Propellers when the old one was an aluminum prop

[This message has been edited by youri_bujko (edited 25 July 2001).]

[This message has been edited by youri_bujko (edited 25 July 2001).]

[This message has been edited by youri_bujko (edited 25 July 2001).]

[John Kennett]

Doesn't sound good to me. I would expect rather more than 30 knots from that combination (I had a 5.7m RIB with a 115hp outboard, and it would do 45 knots flat out).

Was there a particular problem that meant you needed the hydrofoil?

It might be worth experimenting with a stainless prop to see if that gives better results.

John

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John Kennett
RIBnet

[Alan Mckewan]

I have some experience of the effects of these hydrofoil atachments. Firstly, the Zodiac ? Bombard ribs are are good strong boat but are quite heavily built up and could be expected to be a bit slower (and more comfortable!) than some others. I wouldn't expect more than 37/38 knots out of your combination without a special prop and / or engine raised. Fitting of a hydro-thing could be expected to lose 3knots on a 60HP and probably 5 knots on your rig. So you are still losing more than you should. Yuo need to rule out the effect composite prop effect. I would try a (borrowed) 17 alloy or better still dispense with the hydro-thing and correct any attitude problems with weight, console position or trim tabs.

[zod550]

i also have a zodiac 550. it has a 100hp 4 stroke yamaha with a 19" stainless. when i first tested the boat it had a 115hp suzuki and it did approx. 40 knots with 2 big guys. with a 19 inch prop. with my 4 stoke i have experimented with 17-21" prop and i think the 19 " is right. i can do 35 knots with 2 people. you may want to think about raiseing your engin up. most of the time the engin is installed with the cavitaion plate even with the bottom of the hull but you can go up a few inches which is a lot less drag. i also had a wing on my boat but instead i had a couple of trim tabs made up(non adjustable)and it works a lot better. lot softer landings coming off a wave. chris