Increasing boat speed

[Hula_Grub]

Yes it was. Very similar situation to the OP where I was under-powered. As I posted earlier, I had a 25hp on a 16 Lund Rebel rated for 45hp. With just me in the boat it worked fine but add another full-size adult and I struggled to plane out. Added the hydrofoils and I could get up on plane with two additional passengers plus with the added lift it gave me, I was able to trim it out one more notch and my top end speed gained a small amount, like Harvey, about 2mph give or take.

This sums up my experience exactly...

Sonicrunch, I do plan on looking at other props for the new motor at some point, but my performance is adequate at the moment.

No prop is is perfect for all conditions. Airplanes and big ships have variable-pitch props for a very good reason.

[pulsar_nx]

I've had hydrofoils on all of my boats.

14' alumacraft bench boat with a 9.9hp johnson would go 15mph with it vs about 10 or so without.

Second 14' sylvan super snapper with a 25hp johnson would do 30 with and porpoise violently without.

And my current a crestliner cx1650 alum bass boat with a 25hp 4stroke evinrude will do about 20 with and hop up on plane quickly and 23 without but takes awhile to get onto plane and sometimes can't with enough load, like an extra person or two.

Small light boats fair far better than large boats with foils. On a larger boat(adequately powered) the only reason to use one would be to ski or tube.

[Mike Stark]

I have a 16ft Lund Rebel with a Yamaha 25hp 4 stroke. The 25hp motor allows me to head into the some of the lake in the BWCA. The motor is under powered for the boat. Like others have said, it is fine when I am by myself but once i put another person in I loose top end speed and hole shot. A third person in there and we are creeping along.

From what iv read it sounds like a hydofoil might do the trick for me.

What hydrofoil have people had the best luck with?

Thanks.

[Down Deep]

Here are some things you can do, but it will cost you.

Install a jack plate to raise the engine after you come on plane.

SS Prop

Power trim and tilt.

I had a hydrofoil on a 40 HP and took it off. I didn't really increase the speed that much and made the tiller control harder. I put a SS prop on the boat and gained far more that I got with the hydro. You could also call Soderbloom Props out of Cromwell MN and ask what sort of propping changes could be of a benefit.

[BobT]

Well, I had opportunity to run my test as promised and here are the results. Note that this was a very limited test and is not conclusive in any way but enough to convince me.

Previous history

Boat: 1993 Lund Rebel16

Max HP Rating: 45hp

Outboard: 1973 Evinrude 25hp

Hydrofoils: Dolphin

When I first got the boat I found that it took a long time to get up on plane. It was just too under-powered with the 25hp. After installing the hydrofoils, the boat was able to get up on plane much quicker. Additionally, I was able to trim out the outboard one more notch, which helped gain about 2mph in top end speed plus improving the ability to handle a little heavier load such as one more passenger.

Current test

Boat: 1998 Sylvan 1600 Adventurer

Max HP Rating: 90hp

Outboard: 2011 Evinrude E-Tec 90hp

Hydrofoils: Dolphin

This boat is equipped with an outboard matching the maximum rating for the boat so it is fully powered. When I got this boat it was already equipped with hydrofoils and when I upgraded to the new E-Tec last spring they transferred the hydrofoils to my new E-Tec. The best speed I could get out of my boat last summer with one extra passenger, according to my GPS, was about 38mph give or take a tenth or two.

Last week I removed the hydrofoils from my outboard. Yesterday, I took the boat out and since it was nice and calm I decided it would be a good opportunity to see if there was any change in boat handling or speed. My 15-year old daughter was with me so I had one extra passenger.

** Hole shot: I was unable to notice any discernible difference getting the boat up on plane.

** Handling: I did feel a little less resistance, although subtle, with the steering wheel so it appears that the hydrofoils do add some resistance that can be felt at the steering wheel. I suspect this is because you are trying to push the hydrofoils against the water pressure. Otherwise, I didn’t notice any other changes in handling.

** Top End Speed: I played with the power trim and at 5500rpm (full throttle) I the best I could do was h0ld 38.2mph according to my GPS. That’s about the same as with the hydrofoils installed so no discernible difference noted.

Summary: When a boat is underpowered the hydrofoils can be helpful with both hole shot and top end speed. However, with appropriate horsepower they don’t seem to make much difference and in fact seem to add stiffness in steering. I expect they may be helpful when the boat is loaded heavier though.