Loss of top end revs under power - now me!

[blan321]

Yanmar 2GM 20 seawater cooled. Only reaching 3100 in gear. Reaches 3800 out of gear briefly. Should and did reach 3400 and even 3600 last year for short periods in gear.
Engine out this last winter, no internal work (fuel tank) but waterways cleared etc. New exhaust hose from manifold. Elbow was excellent.
Only launched 3rd May, not sure where to go next. Could barnacles on prop have grown and caused this? Polished prop, same as last year, same marina (chichester).
Any advice gratefully received, thanks

 

[cmedsailor]

Could barnacles on prop have grown and caused this? Polished prop, same as last year, same marina (chichester).
Any advice gratefully received, thanks

I am sure you will get more wise answers, but you can start from this. It's summer, a quick dive and you can check this easily.

 

[johnalison]

A small waterproof video camera is worth having, though conditions may not allow you to see only moderate fouling.

 

[KeithH]

Only launched 3rd May, not sure where to go next. Could barnacles on prop have grown and caused this? Polished prop, same as last year, same marina (chichester).

I would suspect tubeworm rather than barnacles - My friend's boat had a large "infestation" of tubeworm last year (in Chi Marina as it happens), and that had a major effect on the maximum revs of the engine in gear. It also caused a tendency to over heating of the engine, and some black smoke at max revs due to the extra load. However, May to July is a bit of a short time for much tubeworm growth.

Another thought - have you got a rope cutter on the prop? If so, I wonder if some polypropylene rope might have fused itself to the propcutter?

Why not dry out at one of the Itchenor piles, and have a look at the prop?

 

[blan321]

Thankyou to the comments, all helpful. I took her down to below itchenor this afternoon, anchored and dived
Prop covered in tubeworm casts (?), all scraped off with paint scraper, drying at itchenor tomorrow to antifoul the ptop, giving up on polishing!.

 

[blan321]

Forgot to say that has cured problem, engine revs fine on way back to marina!

 

[blan321]

Just to add, I dried out next day at Itchenor, applied hammerite special metals primer (that I have used before on aluminium too) followed by 3 coats Velox. Couldnt give it the specified 12 hrs drying time as even K. Canute found.
Checked next day, after full revs back to marina and to easthead next day, hasn't fallen off (yet). Hopefully will give a good result, thank you to those here who have used and suggested these paints.

 

[KAL]

Hope you have success with it. Vyv’s suggestion of the Hammerite was good, but the Velox steadfastly refused to adhere to it. The Hammerite, however, stuck unfailingly to the prop. Am now using Hempel’s Silic One. Hope to lift in a few days to see how that has fared after a year.