Should I hydrofoil on a Tri-hull?

[Ki Ki]

I have a 50 hp Johnson from 1970 on an old tri hull boat. It's slow to plane, but engine runs great.

Should I add a hydrofoil? Would it be helpful--- are they tough to install?

If anyone knows of a good one at a good price to purchase can you provide a link?

Thanks all, wasn't sure if these are just myth or really work.

 

[cougar1985]

Re: Should I hydrofoil on a Tri-hull?

whats the rated hp of the tri-hull?id go with nauticas trim tabs they work great.

 

[Ki Ki]

Re: Should I hydrofoil on a Tri-hull?

whats the rated hp of the tri-hull?id go with nauticas trim tabs they work great.

Rated at 70 HP, has a 50 hp.

 

[eavega]

Re: Should I hydrofoil on a Tri-hull?

Hey

So we have a very similar setup; I have a 15' tri-hull rated for a 70 HP running with a 50 HP. I've found it to be a tad underpowerwed. I've stepped down the prop to a 13p and I now at least get the motor running at 5800 RPM at WOT, but it is now a dog out of the hole. My motor had the Attwood Hydro-stabilizers. I find that it may allow the boat to plane up a little quicker, but it doesn't work as advertised in that the stabilizers are supposed to ride out of the water once you get on plane, and mine are still in the water. I am assuming that staying in the water has two effects; 1. it causes additional drag, slowing the boat down and 2. it makes turning a little scary since it seems to want to force the boat to either run perfectly flat, or to continue to lean in the direction of the turn. I have ordered the Nauticus smart tabs and am patiently awaiting their arrival next week so I can install them and give that a try. Given what I know about hydrodynamics, the smart tabs seems to me to be a better solution to increasing the planing area of the boat. I will let you know what my results are next week.

Rgds

Eric

 

[ajgraz]

Re: Should I hydrofoil on a Tri-hull?

Got some home-made (though not adjustable) trim tabs on my 15' tri-hull:

(I think you can see them in the lower left. Made from aluminum angle, aluminum plate and stainless hardware.)

With all the weight from batteries, fuel tank, bait tank, etc. making this boat so butt-heavy, I found those to really help getting on a plane.

 

[CaneCutter79]

Re: Should I hydrofoil on a Tri-hull?

My Attwood stabilizers ride out of the water once on plane. It does help on hole shot but I would not say it's a dramatic improvement, only a noticable very improvement.

I agree, it's all about the prop setup and motor height setup. Your cavitation plate should be right around the water plane at WOT. If not, you're too low. If it's too high, the caviation plate is way above the water plane but that doesn't sound like your problem.

Sounds like you need to check your WOT rpm and then go from there. You may have a prop with too much pitch.

I dropped from a 19 to a 17 3-blade with more rake angle and cup and my hole shot is slightly better but I have a lot more lift and the prop will not slip at WOT because of my motor height setup for my boat. It's a 15ft modified-V (a type of tri-hull) with an 85hp Evinrude. I get about 39mph average and sometimes 40-42mph depending on chop at 5,100rpm. It's just a tad over-propped but my hole shot is on plane in 4 seconds so not bad.

 

[ozarkt165]

Re: Should I hydrofoil on a Tri-hull?

I have a 76 ozark 16ft tri hull w 76 Johnson 70 hp. Hull rated for 115hp. That would be nice....lol last 2 years had trouble getting out of the hole if i had a extra 250lbs beside me. Had to have people in bow or it would just stand up and push. I would actually have to stand up to see over the bow. Added a stingray series II hydrofoil this spring, made a world of difference! Boat jumps out of the water. It increased my loaded top speed from 26-28 to 32mph. Solo top speed remained at 34mph. The foil is right at water level when on plane. Know a guy that used to build props need to track him down and have him rework my prop.

 

[dforest]

Re: Should I hydrofoil on a Tri-hull?

I have a 1973 (I think) Bomber bass boat with a 70hp Johnson which would stand up and plow along before planing. I added a SE Sport 300 hydrofoil and it pops right up with minium bow rise. It was very easy to install and very dramatic improvement.

 

[eavega]

Re: Should I hydrofoil on a Tri-hull?

Providing a little further information here. My smart tabs arrived yesterday, so I have not installed them. I did take the boat out to the lake yesterday evening. I had removed the hydrofoil just to see how the boat handles without the fin. My observations; She is now a total pig to plane. No hole shot at all. Like trying to get a Yugo to run at the speed limit uphill in a headwind. It would not plane reliably when loaded. We were two 200 Lb guys, with some additional gear (extra battery, extra anchor, fishing gear, and cooler), and sometimes the planing gods were with us, sometimes not. I couldn't figure out the magical formula, but I think it may have to do with either a tailwind, or shifting weight around. We went back to the dock and dumped the extra battery (actually a 29HM deep cycle battery, so figure an extra 60 or so pounds there) and the anchor (8 Lb danforth anchor with 20' of chain, so we may figure another 15-20 Lbs all told there, so we dropped off a child, weight wise) In the boat by myself, planing was not an issue, so it is definitely a weight and balance thing. On the flip side, when it did get on plane, the boat was running 27 MPH, and turning much more smoothly. So the end effects of running with the hydrofoil is:
1. Faster, more reliable planing.
2. Loss of speed (approx 3-5 MPH) at top end
3. Less ability to comfortably carve turns.

I will report back next week after I install my smart tabs, and take the Plantain out for a shakedown cruise.

-E

 

[eavega]

Re: Should I hydrofoil on a Tri-hull?

I will report back next week after I install my smart tabs, and take the Plantain out for a shakedown cruise.

Okay, reporting as I said I would. I ran the boat with the 13p prop. We were two people aboard, combined weight somewhere about 450 Lbs, plus fishing gear, battery, cooler. Lets figure the total weight on the boat at about 550 Lbs. Set the trim tabs to the 4th hole, and the manual trim on the motor to the 3rd hole. The boat will now get on plane in less than 8 seconds, and runs at 28 MPH @ 6K RPM WOT. Cruises comfortably at 21 MPH @ 5000 RPM. Tracks straight in the water. Turns are smooth. All in all, I believe the Smart Tabs have given this boat to reliably move over 500 LBS in passengers and gear as well as the 50 HP is going to push it. I would definitely recommend you try the smart-tabs to resolve your underpower issue. I am very satisfied with the performance change in the boat.

Rgds

Eric

 

[ondarvr]

Re: Should I hydrofoil on a Tri-hull?

When using a foil the idea is to raise the motor until the foil out of the water when on plane, otherwise its kind of a waste of time and may create the handling problems you experienced.

What you did was correct for your problems though. Have you checked the foam in the hull to see if its waterlogged?

 

[eavega]

Re: Should I hydrofoil on a Tri-hull?

What you did was correct for your problems though. Have you checked the foam in the hull to see if its waterlogged?

If you are asking me, yes. I cut through the deck in a couple of places looking for saturated foam and found none (actually I found no foam. I suspect that this boat may have had its deck replaced at some point in its history). I think that like the OP, my hull is rated for a 70 HP, and the old 50 is a hair underpowered for this hull. Also, I never experimented with the trim holes (manual trim), but read on another thread that its a good idea to try and trim out the motor if the hull is on the heavy side, especially if its bow-heavy. Perhaps if I had the hydrofoil on the motor with the motor trimmed out (instead of all the way in as it was) it would've worked as designed. As it is I am very happy with the smart tabs, and the hydrofoil is not going back on the motor.

-E

 

[ondarvr]

Re: Should I hydrofoil on a Tri-hull?

Raising the motor means unbolting it from the transom and moving it up (different bolt holes), the trim angle is something different. Raising the motor on the transom may get the foil out of the water, which reduces drag and may increase the speed.

 

[Joshua Nichols]

Re: Should I hydrofoil on a Tri-hull?

Put one on.. I had a tri-hull and installed one.. Very easy to put on... I used the attwood from Wal mart.. Cheap.. Made a difference.

 

[eavega]

Re: Should I hydrofoil on a Tri-hull?

I have a slightly used one for sale right now on craigslist . Need to offset the cost of my smart tabs!

-E

 

[eavega]

Re: Should I hydrofoil on a Tri-hull?

Raising the motor means unbolting it from the transom and moving it up (different bolt holes), the trim angle is something different. Raising the motor on the transom may get the foil out of the water, which reduces drag and may increase the speed.

Gotcha. Yeah, that might have worked too, but seems like a lot more effort .

 

[CaneCutter79]

Re: Should I hydrofoil on a Tri-hull?

Gotcha. Yeah, that might have worked too, but seems like a lot more effort .

Yep, for a 50hp motor, you're doing about all you're going to do. As for me, my foil is out of the water on plane and helps increase my prop's traction (very little slip ratio). If I raise the motor, the prop slips more (looses traction) and I have less bow lift. The boat actually runs 2-3mph less with the motor raised or without the foil.

It's all about motor/hull/prop setup. There is a balance to be acheived between the horse-power, the prop, and the hull type, shape, length, weight, etc. Overall, I bet 70% of performance issues are related to props but mainly because they the rig is either over propped, under propped, or the wrong prop type for the hull.

Sounds as if you have a good thing going with your tabs but they will probably add drag and decrease your fuel economy slightly. The tabs are pushing down and dragging causing your stern to lift up which also forces the bow down. If you ever increase your horse power to the larger motor, remove the tabs and try a prop recommened for your hull type and weight. If you're happy and the boat is performing without guzzling at the gas pump, run it and be happy.


For anyone else with a tri-hull and looking for increased performance, I thoroughly recommend the Turbo1 stainless prop. Excellent hole shot, performance, and excellent bow lift right out of the box and it's a lot cheaper than most other new stainless props. My top end has stayed about the same by dropping from a 19 to a 17 but on a good day, I'm actually faster (41-42mph) because I have much more hull out of the water and a lot of bow lift for a tri-hull. The benefit was the fuel mileage. It almost doubled. The Turbo really pushes the boat well and almost NEVER slips! It only slips slightly when my 290lb fishing bud is with me and we're over loaded with gear. (haha) If we push all the gear to the back, it gets on plane within 8-9 seconds and doesn't slip. My top end only looses 1-2mph even with all the added weight.