TAMD41P Max revs

[R400]

Our MF 805 200brake Volvo runs at 4200 revs WOT , pulls 24 knots on the gps and runs cool. I'm sure I read somewhere that the max operating is 3800 revs. The prop is 20 x21 pitch and at idle the boat travels at approx 2knots. We bought in Ireland where it was used primarily on the river Shannon hence lower speeds required at tick over my suspision is the prop is under pitch to allow this. What does the jury think?

Don't get me wrong we love the performance but with 850 hours on the clock don't want to stress the unit ,but it's pretty handy for running through the stacks before the over falls get looney.
Many thanks

 

[volvopaul]

Our MF 805 200brake Volvo runs at 4200 revs WOT , pulls 24 knots on the gps and runs cool. I'm sure I read somewhere that the max operating is 3800 revs. The prop is 20 x21 pitch and at idle the boat travels at approx 2knots. We bought in Ireland where it was used primarily on the river Shannon hence lower speeds required at tick over my suspision is the prop is under pitch to allow this. What does the jury think?



Don't get me wrong we love the performance but with 850 hours on the clock don't want to stress the unit ,but it's pretty handy for running through the stacks before the over falls get looney.
Many thanks

Sounds like your underpropped but to check for sure I'd use a handheld tachometer to check the true rotational speed before your go spending on the prop, or just watching the taco and don't go over 3800.

 

[Racingfrank7]

Our old MF805 with a 41 did exactly what you also describe, speed revs the lot.
But last 3 years I knew it was on the south coast not Ireland.
Maybe common fault or common to under prop ?

 

[Latestarter1]

Sounds like your underpropped but to check for sure I'd use a handheld tachometer to check the true rotational speed before your go spending on the prop, or just watching the taco and don't go over 3800.

Paul,
Interested in your comment about not going over 3,800 rpm, no high idle spec for VP 41 but assume it must be around 4,180 rpm out on the governor droop.

With 50% tanks and a clean bottom I have always had a liking for being able to make high idle to prevent engine overload when hull becomes fouled, is the VP 41 an exception to this rule?

 

[R400]

Bit fuzzy on what high idle is

 

[Chris_d]

My manual states 3700-3900 as WOT revs for AD41P, my boat has AD31P's which are basically the same engine with only 4 cylinders and limit is 3900-4100 so I doubt you are doing damage just a bit under propped.

 

[Latestarter1]

Bit fuzzy on what high idle is

Diesel injection pumps develop max power therefore max fueling at manufacturers rated speed in this case 3,800 rpm, however fuel is not shut off abruptly at rated rpm it is gradually reduced up to the governor cut off point (high idle), this is called the governor 'droop'. For marine engines governor droop is around 10% in order to benefit constant rpm governor stability.

A mechanical diesel engine must always be able to make high idle no load to ensure throttle linkage is correctly set up.

 

[Shirley Knot]

I agree, it sounds underpropped. I think we make 4100-4200 WOT no load on KAD43's, but they should make 38-3900 max under load. Cruising garbage and growth will reduce that (and top speed), but even so...

 

[Latestarter1]

I agree, it sounds underpropped. I think we make 4100-4200 WOT no load on KAD43's, but they should make 38-3900 max under load. Cruising garbage and growth will reduce that (and top speed), but even so...

I am not a Volvo Penta person and have no clue how out of whack their tachometers can be, however heed Volvopaul's words regarding 'calibrated'.

One cannot make a glib statement regarding engine load and propeller pitch without knowing if readings are truthful.

 

[Shirley Knot]

Well, we had a similar issue but with the boat apparently overpropped, and had someone calibrate the tachos. They were within 2%...