Effect of marine growth on performance

[pcatterall]

Just spent fun time trying to clean my hull from mussel type growth.
We were sailing last week and seemed a bit slow under sail but very slow at our cruising revs when under engine.
I was convinced that the problem would be mainly growth on the prop but found it fairly clean. The rudder had a lot of clusters on it and the hull especially where if shapes down to the prop.
Just trying to get my head around the issue, is there a difference in water flow behaviour and performance under sail or under engine?

 

[bbg]

I suspect the performance drop under engine is more noticeable because you have a benchmark. You know that X revs should equal Y boat speed.

Much harder to say that we "should" be going Y boat speed in certain wind conditions, unless you have spent the time really benchmarking your performance.

 

[Grumpybear]

Just spent fun time trying to clean my hull from mussel type growth.
We were sailing last week and seemed a bit slow under sail but very slow at our cruising revs when under engine.
I was convinced that the problem would be mainly growth on the prop but found it fairly clean. The rudder had a lot of clusters on it and the hull especially where if shapes down to the prop.
Just trying to get my head around the issue, is there a difference in water flow behaviour and performance under sail or under engine?

As a corollary to that, we last had our boat lifted and antifouled exactly two years ago. Last year we noticed the expected loss of speed under both sail and power, but in the last twelve months there has been no noticeable further deterioration in either mode, though the hull does appear to be dirtier. We use Hempel hard racing white, so fouling is obvious!

Any thoughts about that, and apologies for thread drift.

 

[ex-Gladys]

When I bought Gladys in 2005, I made an offer subject to sea trial and the first one "failed" due to fouling. The cause on lift out was tube worm over the prop and a ball of mussels about 3ft by 18" under the keel. Absolute flat out with a 47hp engine was 1.2kts... Fouling can have a major impact

 

[Birdseye]

I suspect the performance drop under engine is more noticeable because you have a benchmark. You know that X revs should equal Y boat speed.

Much harder to say that we "should" be going Y boat speed in certain wind conditions, unless you have spent the time really benchmarking your performance.

I unintentionally did that test running the engine at fixed revs before and after a pressure wash and in non tidal waters on the same morning. On my 35 footer the difference was 0.75kn. And the hull had some slime and weed but no crustaceans.

 

[Hipchick]

It always slows you down. We picked up a fertiliser bag off Cuba. Couldn't work out why we couldn't steer and were down to 1knot. It was in a storm of course. When we had daylight MLH went under the boat, found the fertiliser bag wrapped round the prop and full of sargasso weed. Cut it away and we were off again.

 

[fergie_mac66]

Re: Effect of marine growth on performance,

I have not tried oysters soi really cannot say the effect they have on performance

 

[LadyInBed]

Re: Effect of marine growth on performance,

I don't A/F as I moor on a river and get half fresh and half salt over the hull ( boat stays in all year).
I need to pressure wash and scrape a bit to clean off the hull twice a year.
When it's in need of being done I loose a good knot.

 

[William_H]

Re: Effect of marine growth on performance,

I live ina localle of rapid fouling growth. Warm water and sunshine. Yes fouling has a huge impact on performance the smaller the boat the bigger the impact. You notice the impact most in sailing to windward in lighter conditions. You really notice if you are racing against others. olewill

 

[Daydream believer]

Re: Effect of marine growth on performance,

My boat has coppercoat & it allows a lot of slime ( followed by weed growth of 2inches or so very soon after)
This has a marked effect on speed. It also causes a lot of weight on the tiller when motoring
One year at full engine revs the tiller was really hard to hold & the stern sunk by several inches as the engine tried to push against the resistance & caused massive propwash on the rudder. I had the boat lifted mid season & jetwashed & the boat was a joy to sail again
Any sort of growth slows the boat

 

[pcatterall]

Yes I suspect it was just that we know exactly what speed to expect using our cruising revs in calm conditions.
Thanks all.

 

[johnalison]

Yes I suspect it was just that we know exactly what speed to expect using our cruising revs in calm conditions.
Thanks all.

I was much happier in the olden days before I had an accurate speed log.