Propellers

[Montemar]

Is it better to be slightly under propped or slightly over propped for a boat with half fuel and water and a months fouling?

 

[Bouba]

Is it better to be slightly under propped or slightly over propped for a boat with half fuel and water and a months fouling?

Can’t you clean the hull while you’re changing the propeller ?‍

 

[Portofino]

Under .It should have been manufactured under in the first place .
When it’s all clean and new ( like MBY test ) it should reach about 3 % over rated rpm .

“Fouling” is I presume both props + hull ?
Depending on the degree of fouling , the weight of the boat its best to back off he revs to reduce the EGTs .Other wise they will soar to dangerous levels, definitely be elevated .
What boat and engines are we discussing and has it got its manufactures props ?

 

[Bajansailor]

It is best to be careful and cautious, and not try to reach the full theoretical revs at all.
As Porto says, you do not want high exhaust gas temperatures.

 

[scottie]

Under would be more logical

 

[Montemar]

Broom 33, TAMD41B, 20D x 23P x 4 and not as manufactured. Was originally under propped with 20D x 22P x 3 and now is over propped. The boat initially was supplied with TMD41B engines and then fitted with aftercoolers but it looks as if the props were not upgraded. Broom say that 20D x 26P x 3 was the last size fitted but did not say which engines but I assume TAMD41 something.
I will get props re-pitched. I am inclined to err on the side of being under as appears to be favoured so far.
I have just bough EGT sensors and will fit as soon as possible though driving to the marina not exactly an essential journey at present!