Speeding up my Hydrasports/140 Evinrude - Hydrofoil? Advice?

[ghostwave]

So I've been working most of the summer - off and on, on my 1981 Hydrasports 2100 CC (Center Console). It's a Kevlar hulled boat and weighs 2100 pounds. Originally, it had a Johnson 235 on it, but that motor was shot, so I took a solid 1977 Evinrude 140 that I had on an old Renken 19 footer (only 1300 pounds) and put it on the Hydrasports. The motor originally had a 3 blade prop that I think had at least a 17 pitch (maybe even 19, there were no markings on the old prop), and it would put the Renken on a plane, even fully loaded, in nothing flat, and go as fast as I felt comfortable going. The prop was pretty chewed up though, and when I put the motor on the Hydrasports, it would cavitate - because the motor was a bit higher out of the water than it was on the Renken. So I put a 4 blade 15 pitch Solus prop on it and at the recommendation of the Solus guy. I've now got the entire rig running pretty well on the heavy Hydrasports, but the boat is, as you might suspect, slow. I've fixed the tachometer and at Wide Open Throttle, it's running at 5000 RPMs but still struggles to get on a plane and noses up a good bit. There's no cavitation with this new prop. My speedo isn't working but even when it planes out, I don't think I'm getting more than 20Mph out of the boat. If it's just me driving it, it'll plane out after 15 seconds or so. If my wife and two small kids are up front, it does about the same.

At the recommendation of a boating buddy, I'm strongly considering a hydrofoil like the SE Sport 300 SPORT MARINE TECHNOLOGIES SE Sport 300 Performance Marine Hydrofoils at West Marine

I don't care if the boat goes real fast, but I want and need it to go faster than it is.
So I suppose my questions are:
1. if I'm getting 5000RPMs at WOT, does it make sense to go with a bigger pitched propellor?
2. These foils seem to help folks in my situation. Anyone have any experience like mine and can offer some advice ?
3. Is the motor (which tests 120 on all cylinders), just not powerful enough for the heavier Hydrasports?

Thanks very much.
Chris Dixon

 

[fireman57]

Re: Speeding up my Hydrasports/140 Evinrude - Hydrofoil? Advice?

The hydrofoil will only help with planing the boat not speed. You will pick up around 100-200 rpms for each degree in pitch that you drop depending on your setup. If you are running 15pitch now you can drop probably to a 13 but it will probably not increase your speed a lot. It will bring your rpms up to where that engine should run and help your hole shot. Like it or not a 140 isn't going to go like a 235. You might get better results posting this in the prop section.

 

[JB]

Re: Speeding up my Hydrasports/140 Evinrude - Hydrofoil? Advice?

Yes, 140 is not enough power for that boat.

 

[ghostwave]

Re: Speeding up my Hydrasports/140 Evinrude - Hydrofoil? Advice?

The hydrofoil will only help with planing the boat not speed. You will pick up around 100-200 rpms for each degree in pitch that you drop depending on your setup. If you are running 15pitch now you can drop probably to a 13 but it will probably not increase your speed a lot. It will bring your rpms up to where that engine should run and help your hole shot. Like it or not a 140 isn't going to go like a 235. You might get better results posting this in the prop section.

Agreed - put it in the prop section - and I know I won't get anything near the speed of the 235. But with the 235, the damn boat was almost too fast. And I know why they called em 'Two Thirsty Five's". I reckon a foil is a cheap way to test as a last resort before I sell the Rude. It's just that I'm attached to it. It was the motor my granddad taught me to work on and took me fishing with.

 

[fireman57]

Re: Speeding up my Hydrasports/140 Evinrude - Hydrofoil? Advice?

Sounds to me like you should keep the engine and find another boat. Good luck.

 

[metriccrescentwrench]

Re: Speeding up my Hydrasports/140 Evinrude - Hydrofoil? Advice?

Sounds to me like you should keep the engine and find another boat. Good luck.

Yep. We have to assume that boat was rated for at least 235 hp since that's what was on it. With a 140 it's quite underpowered.

But with the 235, the damn boat was almost too fast.

"too fast".... what's that?

I'm not positive about a '77 140, but I believe that 5000 rpm is kinda' low for wot. You might be able to get a better hole shot by dropping the prop pitch a little bit more. I definitely wouldn't go to a higher pitched prop, that would more than like slow you down because the engine wouldn't be able to make full power at a lower rpm.

IF you can live with whatever top speed you arrive at with a prop that will get you to the recommended upper rpm range, a foil would probably help you get on plane quicker. As has already been stated it's not going to help your top speed at all.

 

[MaPaHa]

Re: Speeding up my Hydrasports/140 Evinrude - Hydrofoil? Advice?

I am kind of partial to my old 140 Evinrude that must be about the same year except it's the green and white color. Maybe it's a year or so older but I know its late 70's. I had it on a party barge for several years but wasn't fast enough to ski behind so I changed it to a mid 90's Johnson 150 and believe it or not, I went from about 30 ish to nearly 40 mph. I can say a solid 7.5 mph gain and close to 10 mph in some conditions. Those old motors are rated at the engine and after much research before changing the motor I found that 140 bubble-back motor went to the 115 hp model after the re-rating took place in the mid 80's. I suppose they could have de-tuned it a bit and produced it as a 115 but I can tell you for sure there's more than 10 hp differance between the two motors. I have a gut feeling my 140 was around 120-125 hp.

I've run the hydrofoils on about every boat I've owned at one point or another and they work. Even at high speed they can change the way the boat runs and allow you to use more trim in some cases so I would try it if you are leaning that way.

I ran a 4 blade RXB series Power Tech prop that started at 13 pitch and was modified by them to 14 pitch and cupped because it over revved after I added a third pontoon. It was also ported with 5/16 holes for better hole shot. Take off was great.

You can get some improved take off by drilling exhaust ports. After moving my 140 to another boat I had to find another prop (I've still got the 4 blade) so I landed on a SST 3 blade 17 inch and I personally drilled the holes in it for a better hole shot. I used a couple of other props that had factory holes as a pattern. I started with a good 1/8 inch bit and some cutting oil and worked my way up to 5/16 inch holes, but to do it again I would do smaller and work up as needed. Maybe stop at 3/16 inch and try it; then maybe 1/4 inch and try it again. It hits about 4,000 rpm wot coming out of the hole which helps on hole shot. It wasn't hard to do just had to take my time and make a center punch mark that’s exact.

 

[ghostwave]

Re: Speeding up my Hydrasports/140 Evinrude - Hydrofoil? Advice?

So I bit the bullet and bought a SE Sport 300 Foil. Figured it probably wouldn't hurt and might help. Help it did.
Boat now planes out almost immediately and is easier to steer/control. She's still no speed demon but I definitely picked up a little speed too. I'd say probably 4 to 5 mph. I reckon this is perhaps because the boat was taildragging so much before the Foil. RPMs at WOT were around 4900 to 5000. Will do a GPS speed test tomorrow but it seems like perhaps this was worth the $55 I spent on it. If it turns out that my old 235 is still fixable (having my mech buddy check it out this weekend - definitely needs one cylinder head), I'll probably make fixing it a winter project, sell the nicely tuned Rude to pay for it, and spend some serious dough next summer on gas because the Hydrasports will then be capable of 50MPH with the TwoThirstyFive on it.
Thanks for the advice. I'll post up my speed tomorrow.