How many revs do you loose with a seasons fouling ?

DAKA

DAKA

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I had an extra inch of Pitch put on my props last year and I gained 2 knots extra cruise.

Through out the season my governor was cutting in at 4000 rpm.

Time for another inch of pitch I thought,

But last week end I only reved to 3800 (perfect as they are rated 3700 to 3900)

Air/fuel filters all new so it has to be fouling (last scrubbed Feb 06)

So do I have an inch of pitch added which will be perfect for most of next season or do I leave it so I am under pitched early season but still manage max revs at the end of the season ?

I think an inch of pitch will reduce me to 3850 early season but could be 3600 ????????? when fouled
Anyone else notice a foul/rev drop at the end of the season ?

Does 1 inch = 200 rpm ?
 
Early Season 3600 RPM stayed constant up until about end of August WOT 37 Knots VP KAD 32's Engines rated 3800RPM
Havent used the boat for 4 weeks and could only acheive 3300RPM and speed drop to 30Knots.
Engines pull OK no smoke all seems OK normal cruise 2800-RPM 3000 25-27Kts last weekend 3200RPM 27Knots
Shall be doning the diving gear this weekend for a clean up.
when I looked at end of August amazed at the slim build up that remained after a 60 mile journey back from the Solent , prehaps need to change manufacture of Anti fouling.
 
I don't know what the fouling rate is in the cooler UK waters, but if I leave my props for two months without a cleaning, I'll lose >200rpm and the boat will struggle to get on plane. During the warm months a diver cleans mine (and the hull) every 4 weeks. Even with new antifoul (July) I'm getting a few small barnacles on stern gear and hull in 4 weeks.
 
3 months since antifouling and cleaning sterngear. Lost 600 rpm and 6 knots speed. Diver cleaning of sterngear has got most of that back
 
When out for our final blast of the season last week I was pleased to find that I could achive max revs and was only 0.4 knots shy of 30 which we achieved at the beginning of the season. I also only gave her 1 coat of trilux last year so was expecting a to have lost more speed due to growth.
 
Boat out and cleaned off September. Refettled prop fitted, no dings now. Full throttle giving 3600 or so, potentially 200 down but also highest recorded boat speed. Might be dodgy rev counter needing calibration or whatever so dunno really:-)
 
Think a general rule is 1" = 200 RPM

Drop in RPM due to fouling differs from engine to engine.

We drop a short 100 rpm from beginning to end of season, but then again we max out at 2300 at beginning of season... different engines & torque. Guess what you need to look at is % drop to get the equivialent.

If you have tweeked the pitch and have fouled hull, I would not be overly surprised to see the impact which you describe, as the engine works harder at the outset, and fouling therefore will have a higher impact as you are running the engine at the very peak of it's designed powerband.
 
I think you should set the pitch so you get max' rpm with clean bottom.
With the availability of cheap scrubbing facilities in the Solent I would then have the bottom done a couple of times a season or as required.
 
Thank you to all who have replied.

The loss of significant speed by some but maintained high revs must be due to the prop being covered in weed and less efficient so it just slips round without much water being pushed back ????????????

Perhaps speed loss is more due to prop fouling than hull fouling, after all the Hull feels very slippery when fouled .

Next season I will try harder to scrub the props , it's a shame the propspeed stuff as Deleted User detailed doesnt work.

I think I will have an extra inch pitch put on and at least I will have a fast first half season even if I need a mid season scrub as miket suggests, I was to tight this year and almost got away without one.
 
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The loss of significant speed by some but maintained high revs must be due to the prop being covered in weed and less efficient so it just slips round without much water being pushed back ????????????

[/ QUOTE ]

in my case it's because the pitch of the props is related to the availability of power as the hull speed reaches R..ie if I increase the pitch I hit the resistance hump before the turbo comes in - so it never does and I can't plane! I have more power than required (to maintain or even increase boat speed) at peak revs.

Oh for variable pitch props or a 2 speed drive!
 
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...... it's a shame the propspeed stuff as ........ detailed doesnt work.


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Take the boat out of water, clean and dry off... degrease the spinning stuff, get hold of a black Penol 100 pen .... (you know.... the one that gets you high the moment you take the lid off). Use the wide tip to paint your prop with the stuff.

Is reported to work very well against the barnacles... but not sure how eco friendly it is.... Still left to try it our for myself...
 
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