propellors

[AndrewJ]

I have a 39' sailboat and when maneurving in 15 to 20 knot winds, the boat is very difficult to make any headway on the engine alone. I was wondering if someone could give me some advice about a new prop. I had a similar boat a few years ago and the previous owner had put a "power" prop on it. I don't remember what the pitch, diameter etc were, but would appreciate some advice re changing to a "power" prop. I have a 30HP diesel on the boat and even at 2K rpm, with the present prop, it has a great deal of trouble overcoming or even maintaining position in a wind, although in calmn air or water the boat moves well. I'd prefer a slower boat with more "power".
any ideas welcome and thanks.


<hr width=100% size=1>The only easy day was yesterday

 

[dickh]

What is the max revs of the engine? - 2000rpm seems slow, most diesels give max output at 3000 - 36000 rpm - but this will depend on your engine. If the engine spec says, say, max revs under load of 3600, then you should be getting somewhere near this figure, say 3200 - 3400. If you cannot achieve this it sounds as though the engine has a problem.
What will it rev to when not under load?
You may have a fuel starvation problem, could be blocked fuel filters, or a blocked exhaust elbow, or you could be overpropped.
Regarding a PowerProp - I've never heard of this but there are several folding/feathering props available like Brunton Autoprop and Volvo Penta do a similar one.


<hr width=100% size=1>dickh
I'd rather be sailing... /forums/images/icons/smile.gif

 

[Guest]

First Q : Does the engine unload easily when throttle opened ?
Second Q : Does engine NOT unload and revs do not increase - sounds like its pushing hard all time ?

This is good indicatuion of underpropping (first) and overpropping (second).


<hr width=100% size=1>Nigel ... and of course Yahoo groups :
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[AndrewJ]

Thank you for the input. I have had it up to 2100 rpm, but have been reluctant to increase over that. Maybe I'm just babying the engine. I get around 4 to 5 knots at 1700 rpm and am satisfied with that except for the power pushing against the wind. The engine is 1975 with one rebuild 2500 hours ago. (5500 total time). I guess I'll try a higher RPM. As I said, the other boat I had, same make etc, but earlier model had a prop on it which seemed to develop more power, with same RPM. I'll look up some spec on the perkins 4-107 and see what I can find. Thanks again.

<hr width=100% size=1>The only easy day was yesterday

 

[Guest]

Its a 4-107 ?

Give it some wellie then ...... built like the proverbial brick s...house ....

My 4-99 loved being opened up .... pity that other factors took hold and it stopped .... completely remote from this matter.

Honestly - engine like that loves being given stick - open it up and give it a holiday from being bunged up and coking up .... you'll probably have all sorts of black sooty shite come out when you do it - I would keep it going. I always reckoned to give mine a good thrash every so often .........

BTW - my 4-99 is being replaced by a 4-107 .... so water-skiing behind my 25ft Motor Sailer is order of the day ....


<hr width=100% size=1>Nigel ... and of course Yahoo groups :
http://groups.yahoo.com/group/gps-navigator/

 

[dickh]

Definately give it more welly - I suspect you should be able to get over 3000rpm easily but am not familiar with the 4-107. Out of gear it should rev to just over it's maximum, this will give you a good idea of it's max revs under load. If black smoke appears from the exhaust there is a problem - possibly the exhaust injection elbow is blocked. To check this properly you must remove it and check on the bench and clean out if possible, or replaced.
Alternatively have the injectors checked(at an automotive diesel pump place NOT marine - much cheaper).
Also check the gearbox ratio, this g/box may be different from your previous one.
good luck and keep us informed

<hr width=100% size=1>dickh
I'd rather be sailing... /forums/images/icons/smile.gif

 

[Birdseye]

Unlike petrol engines, diesels with mechanical fuel injection have max revs limited by a governor so (assuming that the engine is in good nick and not just about to expire) open the throttle and see what performance you get.

There might well be times when your safety depends on being able to use full engine power, so in a way you are best doing this now rather than mollycoddling your engine only for it to fail when you need it.

<hr width=100% size=1>this post is a personal opinion, and you should not base your actions on it.