does a dirty bum make so much difference

lanerboy

lanerboy

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when we finished all the work on my boat I did a sea trial with volvopaul and we managed 32 knts on a nice flat Southampton water this was back in November, the boat has been in the water since then

we were out in the week on a very flat sea and I tried WOT and only managed 27 knts which is obviously 5 knts down, now could this be down to a dirty bum in 6 months of being in the water

one other thing is a few weeks back we got caught in a pot rope which stopped us in our tracks, now I cut the rope off with a sharp knife and tried the boat straight after and all seemed fine no vibrations nothing out the ordinary so thought nothing more of it,

I have since also put the legs into beach mode and inspected the prop which got caught and all seems fine but I am just wondering has it bent it very slightly that I cannot see and is this what is affecting WOT speed or could it just be she needs her bum cleaning

thanks again
 
Fouling would be my bet. A friend has a 25' Fletcher on the Dart and has the same issue - to the point that it won't get on the plane. It's marginally powered anyway with a 165 Mercruiser diesel, but even just that slimy 'skin' seems enough to take the edge off. He's currently looking at boat-lifts, floating docks etc - basically anything other than a lift 3 times a year! :rolleyes:
 
My boat was in a boat yard last year for repairs. A lot of local commercial boats (particularly fast dive and rod fishing boats) were lifted out there for a quick pressure wash and then relaunched. The yard owner said that they do that two or three times a year as they more than recover their costs in saved fuel and time saved reaching their dive/fishing sites.
 
I remember reading a long time ago about trials carried out on displacement vessels (ie ships) re the effects of fouling, and they found that even an apparently inocuous layer of slime on the hull bottom can knock 10% off the speed.
I presume that the same logic could perhaps apply to planing vessels as well.
 
On my Princess 33 the day it went back into the water after A/F we got 17 knots.
6 months later 12/13 seemed about the best we could get.
 
In the Med ,we do not get this prob as much .-hull slime slowing it down
The sterngear if unprotected / un antifouled ,need scraping every 6 wks ,
The" shells " as they call them impede the prop speed .
Obviously one can dive in and clean the props cos the water is warm ,or if a bigger boat, most marinas have a diver who will do it.
Boats only get lifted once for annual ,anodes+ antifoul.
Planing boats only have a small wetted area when up.
But I guess it's down to engine power and relative weight as wether it can get up in the first place,once slightly fouled .
Someone told me ( particulary in the used mkt) Allways go for the bigger engined boat in a planing boat .
At the end of the season for a given rpm I loose approx 2 knots ,
Ie @ 3000 cruise drops from 28 to 26 ,but I can Allways ease up to 3100-3200 ish if iam really that bothered .
Hull is never cleaned. Just the sterngear - sometimes something to do @ anchor
 
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I have a Princess V42 which I have lifted and cleaned every 3 months.
It's only just slime but it always adds a knot or 2 to top speed.
At start of this season I clocked 34knots full of fuel, water, gear and 7 people.
This weekend just clocked 32 same conditions, due out in next couple of weeks for its quarterly clean. I average 100hrs a year cruising and reckon the wash costs nearly pay for themselves in terms of fuel efficiency.( Plus I lose anodes like they are going out of fashion!)
Empty of everything I clocked 38 knots the year before last which is faster than new!!
S
 
lanerboy said:
when we finished all the work on my boat I did a sea trial with volvopaul and we managed 32 knts on a nice flat Southampton water this was back in November, the boat has been in the water since then

we were out in the week on a very flat sea and I tried WOT and only managed 27 knts which is obviously 5 knts down, now could this be down to a dirty bum in 6 months of being in the water

one other thing is a few weeks back we got caught in a pot rope which stopped us in our tracks, now I cut the rope off with a sharp knife and tried the boat straight after and all seemed fine no vibrations nothing out the ordinary so thought nothing more of it,

I have since also put the legs into beach mode and inspected the prop which got caught and all seems fine but I am just wondering has it bent it very slightly that I cannot see and is this what is affecting WOT speed or could it just be she needs her bum cleaning

thanks again
Click to expand...

It will get slower the day you launch.

Barnacles on the prop will make 6 knots or more difference.
Barnacles on the leg will do similar.

Get Coppercoat and you'll never get a barnacle on the boat, but it will still slime up and slow you down.

You could get youself a RickP of this parish. I needed the slime cleaning off my coppercoated boat and rick offered to go swimming for me. Now I'm not the slimmest though Rick is slimmer than me. Even so, lovely chap that he is, "athlete" may not be the first thing that pops into you head in a word association game.
But......
He used to play competitive water polo!
So with a splash like the wake of a surface drive he goes round the boat with a pan scourer restoring 5 knots!!

Short answer to your question - yes!


Keep your bum clean, legs clean and props squeaky clean. It will save you fuel.
 
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It can make an enormous difference. However I think your fuel consumption at a set rev range is a better indicator as speed can be affected by so many variables. Your higher speed might have been down hill with a wind behind you where as your slower speed may have been the opposite. P&O's Aurora has a sea trial top speed of something like 24 knots yet I have been on watch on her coming through the Dover Straights at 31 knots due to the right currents and tides. I have also seen her max on four engines struggling to make 20 knots.
 
ANDY59 said:
Does anyone know if using the boat on a regular basis , ie once a week , helps to keep the hull and props clean ?
Click to expand...

Hi Andy - Most definitely - I always do a few sharp turns to assist in removing any growth of the hull.
When you mention using the boat on a regular basis - I assume you mean a little further than just from Lymington to Yarmouth :cool:

Hope all had a good time over the weekend with the old gaffers :D
 
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LionsDen said:
Hi Andy - Most definitely - I always do a few sharp turns to clean any growth of the hull.
When you mention using the boat on a regular basis - I assume you mean a little further than Lymington to Yarmouth :cool:

Hope all had a good time over the weekend with the old gaffers :D
Click to expand...
Not as far as yarmouth Terry , that would use to much fuel . Just from the yacht haven to the town quay for a pint .
Old Gaffers was very enjoyable as we happened to meet one of them ;)
 
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