Re: Top Speed Estimate
Go to the BAM www, Go-Fast.com or something like that for their prop slip calculator. Pretty much tell you what you want to know. Plug in what you know like gear ratio (1.87 example), prop pitch (26), rpms (4500)....then go over to the max speed (no slip) and punch calculate, then add your estimated slip number in the slip box and punch calculate on the actual box for the actual speed. The engine/boat/prop combo together have to be tweaked for what you want. With the Laser II on the pad, I'd punch in 15% for slip or maybe less. That's a super prop and on pad your drag in minimal.
The sales brochure for a similar engine of '94 year model shows rpm range to be 5000-5600. I like to run the upper end or just over as I just get better service out of my engine. You are lugging that engine. If you are running the 2 liter block the gear ratio is probably 2; if the big block 2.5 liter probably 1.87 (estimated from '94 brochure similar engines). 26P with a 1.87 is a lot of prop. I think i will submit this answer, reopen on the calculator, punch in some numbers and edit this thread.
On your speed, decreasing pitch will bring up your rpms. It depends on your hull drag and torque curve as to just what this will mean in mph. Normally decreasing pitch decreases top speed, giving more pushing power, but in your case it can result in increased speed. One thing for sure, the engine will love you for it. Additionally you might run some Sea Foam in the fuel for a few tanks at least to clean out some of the crud you surely accumulated for lugging it which may also help to bring up your rpms.
Mark
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Edit per
www.go-fast.com prop slip calculator
Taking your current setup and 15% estimated slip max possible is 59 and actual is 50
Considering 200 rpm per inch of change, dropping down to a Laser II at 22 P yields:
5200 rpm estimate, 58 max, 49 actual.
But if reducing the pitch allowed the engine to move to a different spot on the torque curve, or your boat to water interface improved as a result estimates:
Assuming the 22p allowed the engine to come on up to 5400. That would give you 60 max and 51 actual. If it got you 5600 then max is 62 and actual is 53.
Just for a baseline, if your engine could in fact twist the 26 at 5600 rpms max would be 62 and actual 53.
So, there are some numbers. The slip plays a big part of the equation. A Laser II is probably one of the best props out the in general use giving the least amount of slip. Course slip is load dependent also....how much hull resistance against the resistance of the water is the prop having to push against.
On your current 60mph, you might run your numbers against a GPS system. My Quicksliver speedometer lies to me at WOT. Reads high. In reality, with zero slip which is what you would get in a solid medium (theoretically) you can't get there according to the calculator......but if your gearbox is like 1.76 you could get closer.
HTH,
Mark
