Boating: To hydrofoil or not to hydrfoil

[goteeboy]

I have always just assumed that having a hydrofoil would increase top end, but after seeing these two comparison videos I now have my doubts. If you read his comments, he said he lost 8mph on the top end w/ the hydrofoil.

 

Anyone else do any comparison tests?

 

w/o hydrofoil

 

w/ hydrofoil

[lookinforwalleye]

I have only ever seen them on underpowered rigs!

[craigdritchie]

I have always just assumed that having a hydrofoil would increase top end, but after seeing these two comparison videos I now have my doubts. If you read his comments, he said he lost 8mph on the top end w/ the hydrofoil.

 

Anyone else do any comparison tests?

 

w/o hydrofoil

 

w/ hydrofoil

Hydrofoils won't do anything to increase your top-end speed, and will normally reduce it as a result of increased drag. As lookinforwalleye notes, they're most often used to help underpowered rigs or boats with other specific problems get up on plane more easily.

 

Back in 1992 I was involved in testing hydrofoils for Boatguide magazine. We tested four of them on four different boats: a small Zodiac inflatable with an 8 hp Yamaha, a 16 foot Sylvan aluminum with a 40 hp Merc, a Ranger bass boat with a 150 Johnson GT, and a Freeport 24 (offshore salmon boat) powered by a Merc 150 on a transom bracket.

 

The hydrofoil definitely helped the inflatable, which porpoised all over the place and wouldn't plane no matter what we did with it beforehand. With the foil installed, it stopped bouncing around, and did eventually come onto plane, which was a big improvement. The 16-foot aluminum/40 hp rig was clearly underpowered, and the hydrofoil did improve planing time by a second or two. The only effect the hydrofoil had on the bass boat was to reduce rpm at wide open throttle by a couple hundred rpm, which I suppose could mean some fuel savings over time, but it also cut top-end speed by two mph. Otherwise, it had no positive effect. Results with the salmon boat were basically the same.

 

Overall, the hydrofoils helped the underpowered boats plane better, but did not improve top-end speed. The only real effect they had on the boats that were set up properly to begin with was to reduce top-end speed by a couple mph, and drop engine revs by two or three hundred rpm.

 

For what it's worth, moving to a four-blade (or five-blade) propeller will accomplish the same thing as a hydrofoil, and without having to drill mounting holes in your engine's cavitation plate. They're also less hassle when driving through weeds. Just like the hydrofoil, you may gain lift, but pay for it with top-end speed.

[bigbuck]

Use a different prop to get more top end if that is really what you want BUT, that said, guys looking for a bit more speed usually are underpowered or really need a bigger rig. This is where 2footitis comes into play.

[Terry]

the only time a hydrofoil will increase top end is if your motor doesn't have trim/tilt and you have to keep the pin at the lowest hole to get it up on plane

 

the hydrofoil will allow you to move the pin up a hole or two and still have the power to get you up on plane which will increase your topend

[fishnsled]

For my old 14ft tinny with a 20hp tiller, it made a big difference in getting on plane and overall ride. Was very happy with it. Don't have one on the present boat.

[danbouck]

Smart tabs

[Roe Bag]

An 8 mph. decrease seems excessive. Once installed there is a definite need to adjust the trim. I had a Dol fin on my 14' tinnie with a 25 Johnson on it. It suited my purpose well because when alone in the boat it allowed me to get up on plane at slower speeds. With the bow down at these lower speeds my visibility was greatly improved. When alone in the boat at full throttle it always porpoised. With the addition of the Dol fin the ride was greatly improved. No more porpoising and a softer smoother ride as well. Certainly there is some drag involved but only a matter of a couple of hundred rpm.

I've since upgraded and my new boat doesn't seem to need any improvements. If I were experiencing the high bow syndrome or porpoising, I wouldn't hesitate in installing another.

[POLLIWOGG]

The best I found was Made by Spar and was an aluminum plate with a slight bend at the back. Had it on an old glastron cathedral hull 235 i/o. It would be on plane in 2 lengths of the boat without the up and over you get with a trihull.

 

We put one on a 16ft 145 outboard and it lifted the boat to where it got scary so we took it off.

[Guest Johnny Bass]

I prefer hydrofoil. It takes away a little from the over all speed, but it gets you on plane alot faster especially when your boat is carrying heavy loads. This seems to also reduce the backlash of water overboard on wavy days, so you dont get soaked.

[SRT8 smoker craft]

I put one on my 18.6 starcraft because of porpoising and it solved my problem completely with no ill effects actually gained 1-2mph and no bow rise and on my smoker craft 14 tinny it was a great improvement and it gain 4mph in top speed .

[Cookslav]

I have one on my boat because It had a tendency to porpoise....solved that issue 100%