One for tech guys, and help needed by me Latestarter/VP/Portofino etc

[kashurst]

Re Beyondhelp - I agree with you re petrol engines MAF/MAP etc to control fuel and timing on a petrol engine, because they are generally speed/load controlled by a restricting airflow with a throttle in the inlet path. That's why the ECU needs to know the air mass going into the engine so it can fuel/ignite at the correct ratios

Marine Diesel engines are controlled by restricting fuel not air flow. Diesels are designed so that there is always (almost) more air available in the combustion chamber than required for a given amount of fuel injected. Electronic diesel engines do have MAP sensors and it can calculate air mass flow, but they are there to make sure the engine doesn't over fuel as the load on the engine changes and the turbo pressure build up/slows down. (I could be wrong Its been a while since I worked on them)

Edit, yup the world has moved on, small diesel engines (cars etc) can have MAF units to measure air mass flow as a means of improving control of CO and hydrocarbon emissions if a catalytic converter is fitted.

 

[Anders_P42]

Interesting thread.

I'm sure my boat has been propped on the edge. Anything more than a few weeks growth and she won't hit full rpm at WOT. She will do it after a lift and scrub, 3550rpm on the single D6-370.

With a clean hull she does about 20k at 3000rpm burning 50lph. Volvo quote full load at 3000rpm as 66.3lph, so that means a cruising load of 75% with clean hull. That sounds reasonable if diesels like being worked hard?

With a few months growth, the same 3000rpm will consume 56lph and that means load has gone up to 85%. That sounds more borderline and time for another lift and scrub.

BH, which ECU's do you map?

 

[MapisM]

according the dutch company that did a overhaul on my props in 2013,
prop diameter is 810mm
and pitch is 970 (he didn't specifie the unit, I assume it is mm , is this possible ?)

Sorry B, for some reason I missed your post when I read the one of Beyondhelp earlier.

I'm afraid that those numbers don't stack up, though.
First of all, yep, I can't think of any logical measurement unit for the 970, other than mm.
But that translates into a 38" pitch, which by heart sounds too much for a boat like BA.
Anyway, assuming a 38" pitch and a 1.5 g/box ratio, together with the speed/rpm you mentioned, the resulting prop slip is indeed completely silly.
Of course, you might have tachos not 100% correct, but I don't think they can be so much off the mark.
Besides, I guess you measured SOG speed, but in the Med the STW can't be that different.
Naah, some numbers are bound to be wrong - at a guess, either the pitch or the ratio (or both).

All that said, frankly I wouldn't loose my sleep over the BA props slip, if you excuse the pun.
For instance, in my old tub I don't even know what the props pitch is, and never bothered having it measured.
Therefore, I obviously have no clue about their slip.
When I said before that the slip doesn't change significantly with the load, I could only say that based on a comparison. But how much the % slip value actually is, God only knows - and I couldn't care less, tbh.
Even with the Fountain, whose numbers I previously mentioned, I calculated the slip simply out of curiosity and because I could, not because I could actually do anything about it....