prop turns but minimal boat spped - SailNet Community

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Go Back   SailNet Community > On Board > Gear & Maintenance
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Old 07-03-2011
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prop turns but minimal boat spped

Hi,

I took my boat out this morning for the first time this year. I was on my way to the yard to get it hauled and hull painted. It would go into forward and reverse but at high revs I was only making .9 knts. I can usually easily make 2 or 3 powered by my volvo 25 hp deisel.

It wouldn't have been enough power to deal with headwind so we limped back home.

The boat is a Westerly 26. The motor is a Volvo MD 2B. Wondering about shear pin, prop barnacles, missing blades or transmission problems.

Any ideas would be much appreciated.

Rick
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Old 07-03-2011
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If you're in salt water, or even brackish water, it's probably fouled with barnacles and growth. As well as your bottom. Both will hinder boat speed.
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Old 07-03-2011
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was there lots of black smoke?
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Old 07-03-2011
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Good point sawing. I forgot to mention that. If there is, then fouled prop and boat are very likely.
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Old 07-03-2011
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I had a similar problem, and in my case it was barnacles. I got a scraper for the BBQ - brass brush on one side, scraper at the end - grabbed mask and snorkel, and dealt with it. Was surprisingly easy, unlike dealing with barnacles after they dry out. They ame right off.

It is amazing to me why barnacles grow so profusely (on my boat) in two places - the prop, shaft and strut; and a patch on the rudder which gets the most propwash. Could it be that the propwash blows off the antifouling? and you'd have thought they get dizzy with all that prop spinning...

Anyhow, I suggest a hull and prop clean as a first step!
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Old 07-03-2011
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FYI - some stats on a 35HP power boat in salt water; but relevant nonetheless:

At beginning of test . . . 25.0 mph (40 km/h)
After 10 days in water. . 21.5 mph (35 km/h)
After 20 days in water. . 18.5 mph (30 km/h)
After 40 days in water. . 13.0 mph (21 km/h)

(source: About Boat and Marine Propellers (props))
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Old 07-03-2011
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Thank you. It makes sense to check for some sourt of fouling of the prop and hull first. It is hard to believe that it could slow me up so much but given the numbers you presented and the fact that my boat hasn't been cleaned for two years maybe that is the answer. Am getting it towed tomorrow as it doesn't seem to have enough power to safely manuever around other boats. This is one of those moments when an outboard would be nice.

Rick
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bottem growth is usually the culprit,especially bad if your boat is not taken out often also i've noticed that some areas tend to be worse than others
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It is surprising how a small amount of barnacle growth on a prop can mess with a prop's pushing and pulling power or thrust.
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Old 07-03-2011
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I have a 9' Aquapro inflatable with aluminum bottom and an 8hp Suzuki. She'll do 28mph with a clean bottom. I left her in the water for two weeks and the slime on her bottom prevented her from getting on plane....Scrubbed the bottom.... back to 28mph
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