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Old 07-27-2017, 12:06 PM   #1
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What a difference a clean bottom makes

This season I moved our boat from a mostly fresh water mooring on the Connecticut River to a mostly salt water mooring in Narragansett Bay. The fresh water had kept the bottom pretty clean in Connecticut, but this new location plus a waste treatment plant upstream really made the critters grow.

The bottom, prop and rudder was pretty fouled. So I got a local diver to clean it up. Fortunately Rhode Island still allows diver cleaning whereas adjacent Connecticut does not.

Yesterday we took the boat out for a spin after the cleaning. Wow!! I immediately noticed that the rudder was more responsive at slow speeds. Before I could only get to 15 kts at wot. Yesterday it hit 19.5 and rpms increased from 3,200 to 3,370. Fast cruising went from 12 kts at 2,800 rpm to 15 kts. Even displacement speed cruising at 1,600 rpm increased from 6.7 kts to 7.5.

This is a Mainship Pilot 34 with a single Yanmar 370.

This diver had done a particularly good job. When I kept the boat in NC and had a diver clean it every other month it didn't do this good- maybe a 1/2 knot slower at the fast cruising speed and a knot slower at wot. I will definitely get it cleaned again in September.

David
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Old 07-27-2017, 12:28 PM   #2
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Quote:
Originally Posted by djmarchand View Post
This season I moved our boat from a mostly fresh water mooring on the Connecticut River to a mostly salt water mooring in Narragansett Bay. The fresh water had kept the bottom pretty clean in Connecticut, but this new location plus a waste treatment plant upstream really made the critters grow.

The bottom, prop and rudder was pretty fouled. So I got a local diver to clean it up. Fortunately Rhode Island still allows diver cleaning whereas adjacent Connecticut does not.

Yesterday we took the boat out for a spin after the cleaning. Wow!! I immediately noticed that the rudder was more responsive at slow speeds. Before I could only get to 15 kts at wot. Yesterday it hit 19.5 and rpms increased from 3,200 to 3,370. Fast cruising went from 12 kts at 2,800 rpm to 15 kts. Even displacement speed cruising at 1,600 rpm increased from 6.7 kts to 7.5.

This is a Mainship Pilot 34 with a single Yanmar 370.

This diver had done a particularly good job. When I kept the boat in NC and had a diver clean it every other month it didn't do this good- maybe a 1/2 knot slower at the fast cruising speed and a knot slower at wot. I will definitely get it cleaned again in September.

David
An excellent observation that many do not make.
We have been in LI sound in high growth areas for more than 25 years.
On unprotected (and even some protected) hulls and/or running gear it can make a very large difference in just two weeks.
This type of quick growth is why some engines end up overloaded and with problems without your observations and maybe some EGT gages.
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Old 07-27-2017, 01:51 PM   #3
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In a month in warm NC water, if I don't clean my wheel I can see the effects. One or two knots slower at same rpm. Even the sharkskin on the wheel has an effect, and that is a PITA to scrape. Some divers don't bother with the sharkskin, some do.
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