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

[ghostwave]

View attachment 209987So 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 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. If it's more fully loaded, it won't plane at all.

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 - or at least to get on a plane better and keep its nose down.
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? (That's what I'm really thinking is the issue)

Thanks very much.
Chris Dixon

 

[lexer440]

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

Not familiar with your boat but I had a 1988 evinrude 140vro on my boat with a hydrofoil and it was terrific. Boat was 19' cuddy and weighed around 2500lb, I had a 3 blade 19P which hit max rpm and planed in about 3 seconds from standstill. Top speed was around 70kph.

 

[jestor68]

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

I believe that the 2100 lbs mention might be for the bare hull.

Add the weight of the motor, people/gear, and fuel and I think you'll find your boat weighs a good bit more than you think.

According to the Mercury props selector; if it was running a 135 hp Mercury, it should spin a 17/18 pitch prop and hit close to 39 mph.; using dry 2600+500+40 gal gas.

Why your 140 Evinrude can't cut the mustard is a mystery.

 

[craze1cars]

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

According to prop slip calculator, your current results are not mathematically possible:

15 pitch prop
2:1 gear ratio (I'm making an assumption here...most of those were 2:1...is yours?)
5000 rpm
20 mph

This calculates to 44% slip. That's ridiculous by any standard. For a boat like that I would expect slip somewhere between 12 and 20 maybe? Using 15% slip in a calculator you SHOULD be actually going 30 mph, WELL above planing speeds, if you have provided accurate RPM/prop data.

So you have some data here that is extremely incorrect in where you think you are starting. I will suspect either a DRASTICALLY inaccurate tach or speedo being the most likely cluprits. Or your 140 has been somehow converted to an insanely low low gear ratio...

It would be easier to figure out what to recommend if we start with all good data first so we can see really what you are starting with.

Is your tach pulse setting set correctly for this motor, and is that tach verified correct thru another source? You may think you're turning 5000 rpm, and may actually be turning much less than that, which would explain the struggle to plane and get any speed.

A GPS speed would also be helpful.

I've never had a boat that was improved by a hydrofoil. So they are dismal products in my opinion. If it needs planing help I'd recommend Smart Tabs over a hydrofoil. Not much more money and they work SOOO much better...

 

[steelespike]

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

We know your speed a is a guess so you need to get a gps. Some cells have a gps app.
I also agree some part of your numbers are way off.
Possibly both speed and tach.
Also keep in mind in 77 motors were rated at the power head so your actual hp is probably 5% or so less at the prop.
Still if we compare apples and oranges a similar 140 hp I/O with a 2.00 ratio would probably run a 19" prop
at 35 to 40 mph. with a fair hole shot.at about 4800 rpm.This also makes me wonder why your in a 15" prop?
Is the bottom clean and smooth?no peeling paint?
Is the motor in excellent tune,link and sync,timing set right and advancing as it should?
Throttle opening all the way? Does the boat respond d to up trim?Does it trim down all the way.
Perhaps the boat has absorbed water in the foam under the floor from poor storage or mooring.
If I was going to add a foil it would be a Doelfin.

 

[ghostwave]

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

Man, yall rule. Think I'll get her in the shop to confirm a few things and see where I'm off. Cause clearly something aint right. Thx