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HANUMAN
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I had the boat out of the water a few months ago. Hull was fresh then, and prop was clean. Engine is a Universal M35B, not making any smoke. I've had the boat about a year; this is how it's always been. The throttle is not maxed out....could a tachometer really get out of whack? How do you check that? Other people with the same boat/prop get a lot more speed.
I would check the prop first. Could be growth or fowled.

"a few months" can be a long time. I had my bottom cleaned last august, the diver checked my prop and zinc as well. Said everything was fine. By November when I hauled for the winter my prop was all but gone from electrolysis. I'd post a picture of the prop, but I don't want to scare you.
 

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Discussion Starter · #22 ·
When we were out this weekend, I opened up the throttle all the way while in gear. It went right up to 3000 rpm no problem. I didn't see any smoke either. I didn't check how high the engine would go without a load, though I imagine the max for most engines is around or just about 3000 rpm. To me that suggests that I'm "underpropped", i.e. the prop is not putting enough drag on the engine, and therefore not doing enough work.
 

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When we were out this weekend, I opened up the throttle all the way while in gear. It went right up to 3000 rpm no problem. I didn't see any smoke either. I didn't check how high the engine would go without a load, though I imagine the max for most engines is around or just about 3000 rpm. To me that suggests that I'm "underpropped", i.e. the prop is not putting enough drag on the engine, and therefore not doing enough work.
What is the hp rating of your motor and suggested rpm? Your transmission ratio is important too. I've got a 37 foot Tayana which displaces close to 30000lbs driven by a Perkins 4-108 (50 hp) , Borg Warner tranny 2.1:1 with a 3 bladed 17 inch Max Prop set at a pitch of 14.2 inches. At WOT I get 3000 rpm with 6.8 knots and cruise at 2500 rpm at 6.4 knots all in calm waters. The Perkins in a high rev engine with max continuous rating of 3000rpm and intermitant rating of 4000.
 

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Discussion Starter · #24 ·
The engine is a 35hp Universal M35B. I just looked at the manual, and it said that the maximum RPM is 2900-3000.

I'm thinking I'm going to get someone to take a look at the prop.
 

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The engine is a 35hp Universal M35B. I just looked at the manual, and it said that the maximum RPM is 2900-3000.

I'm thinking I'm going to get someone to take a look at the prop.
Well now lets see. If the engine is really turning max RPM, then I doubt there is anything on the prop. If the prop is clean and the engine turning max RPM, then you're correctly propped. If you're correctly propped, the prop is clean and the engine turning max RPM then you should be seeing the expected speed. A fouled hull or inaccurate speed transducer are the only things I can think of that would make you slow or think your slow if all of the above are true.

The other possiblity is the tach is reading high and you didn't really reach max RPM. If that's the case, you could be overpropped or have a dirty prop but if the prop is the problem, it seems to me you must also have a tach problem.

The prognistications above are guaranteed to be worth at least 3 times the cost. ;)
 
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