Perkins

[Clyde_Wanderer]

Hi, Have any of you forumites got a Perkins Parama 12hp, 3cyl engine in your boats.
I have, and am a bit dissapointed with thespeed I get from it.
Which is aprox 4.5 kts running in slack tide, on full throttle.
Is this an abnormally slow speed? and what could be the cause? Engine seems to run fine, throttle os opening fully, boat weighs 3.25t, and hull is 29ft 6". I know there is a little fouling on prop but hadent expected it to slow her up so much.

 

[ColinHuggins]

29ft6" of what exactly? Your underwater profile will hopefully explain all. And fouling on the prop (unusual) is far less significant than a dirty bottom.

 

[Clyde_Wanderer]

29ft 6" of grp hull, fin keel with part skeg, beam 9ft 6".
She lay in a marina (in the water) for almost a year before I bought her, and that was in feb this year, I havent had it out yet.

 

[cliff]

Sounds like she has a dirty bottom. 18 months in the water? - time for a scrub at least me thinks.

Has the speed dropped over the summer? This year has been quite bad for marine growth.
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"Artificial intelligence is no match for natural stupidity"
sailroom <span style="color:red">The place to auction your previously loved boatie bits</span>

 

[Guest]

Ok ... question ...

When you open throttle does engine unload quickly ? Does she accelerate quickly to the 4.5kts and then just stay there without any change ?

If yes to above then engine is underpropped and reaching prop speed ......

If yes ... you can increase pitch (if space is limited for prop) or best is to increase diameter and pitch giving more drive and speed. I usually look upon it as ... diameter for thrust, pitch for speed.

Dirty bottoms would account for a touch of speed but 1 -2 kts ? Unlikely that level..... 0.5 - 1 kt ok.

4.5kts should be a good cruise economical speed not flat out ...

 

[cliff]

[ QUOTE ]
Dirty bottoms would account for a touch of speed but 1 -2 kts ? Unlikely that level..... 0.5 - 1 kt ok.

[/ QUOTE ]I have experience of one boat that dropped from 6½~7kts down to 2kts due to a "dirty bottom" and all within a couple of months. Never underestimate the effect of weed growth. Boat in question was in the Clyde.
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"Artificial intelligence is no match for natural stupidity"
sailroom <span style="color:red">The place to auction your previously loved boatie bits</span>

 

[Aja]

We have lost a good 1/2 to 3/4 knot so far this season with growth. On the Clyde. I've notice a lot of slime on the hull but no weed. Using Blakes Ocean Performer two pack - boat was launched April. I would consider this normal.

Donald

 

[shamrock]

Our last boat was a 29ft half-tonner, just under 3 tonnes with a single cyl. 9HP Yanmar

When clean bottom and hull, 6kts
Mid season, moderate fouling, 4.5kts. Always dried out for a scrub at this point.

When the engine is only just man enough for the size of boat, fouling makes a really big difference.

Nick

 

[Clyde_Wanderer]

Thanks to everyone who replied to my querie, my hull is very dirty along the water line, but not sure about the hull itself,
one interesting point, my engine does reach full revs straight away( no building up to it), infact there doesent seem to be much difference in boat speed whether the engine is on full throttle or part throttle

 

[cliff]

[ QUOTE ]
one interesting point, my engine does reach full revs straight away( no building up to it), in fact there doesent seem to be much difference in boat speed whether the engine is on full throttle or part throttle

[/ QUOTE ]Duh! mine does the same even with a clean bum but there is a lot of turbulence / prop-wash until the boat picks up speed. I assume you will be lifting her out this winter for anti-fouling etc anyway but if you want to keep using her for a few more months dry her out somewhere and give her bum a good power wash/scrub (and clean the prop and see what the difference is. If you don't have access to a drying out grid / piles go for a lift and hold in one of the marinas unless you know somewhere that you can dryout safely.

Certainly I would think your engine is only just "man enough" for your size of boat so any fouling will noticeably drop her speed.
--------------------

"Artificial intelligence is no match for natural stupidity"
sailroom <span style="color:red">The place to auction your previously loved boatie bits</span>

 

[oldharry]

If the engine is easily running up to full revs without producing much forward motion, then the prop is too small. Its a bit like running a car in low gear all the time. The fouled hull will make matters worse too.