Volvo TAMD 61 A Turbo revs

[Rocksteadee]

I have Volvo TAMD 61 A engines in a Fairline Turbo 36 and am trying to find the slowest economical planing speed
Book recommends 200 rpm below WOT revs. Max revs generally 2700 (I carry gear and half tanks min) which can give 27 kn but so 2500 giving about 23 kn is the recommended but this is a bit juicy on long runs
So.... Next most reasonable would be planning but with turbos just running
From the graphs in manual this would appear to be 2100 rpm
Am I correct in thinking
1. This value is correct
2. The turbos like to be running to prevent smoking and depositing oil and sooting up
These revs gives a speed of about 16 to 17 kn

 

[superheat6k]

I cruise mine comfortably at 16 knots but at WOT with my smaller TAMD60C my top speed is about 22 knots, at 2,900 half loaded with four persons aboard. At 16 knots clean bum and decent cutlass bearings then around 2,200 RPM.

When I was buying the chap who owned Cornish Mead, which has the same engines as yours, reckoned he went everywhere at 16 knots and the engines were really happy with that.

I assume also you have the four bladed props. I would expect your fuel consumption will be around 1.5MPG at 16 knots but perhaps below 1 at 21 knots.

 

[piratos]

I have Volvo TAMD 61 A engines in a Fairline Turbo 36 and am trying to find the slowest economical planing speed
Book recommends 200 rpm below WOT revs. Max revs generally 2700 (I carry gear and half tanks min) which can give 27 kn but so 2500 giving about 23 kn is the recommended but this is a bit juicy on long runs
So.... Next most reasonable would be planning but with turbos just running
From the graphs in manual this would appear to be 2100 rpm
Am I correct in thinking
1. This value is correct
2. The turbos like to be running to prevent smoking and depositing oil and sooting up
These revs gives a speed of about 16 to 17 kn

Hello,
I think you are misunderstanding something. the engines produce max power at wot - If I remember right something like 2700/2800 rpm and its important the boat has the correct props to reach these rpm. But the engine can not cruise with these rpm. Consider the 200 rpm below WOT as the MAXIMUM cruising speed - not the nescessarily the recommended rpm. If I remember right the Turbos cut in well below 2000 rpm, so I do not think you have to bother about the turbos, but there may be others who know the VP better. If you are looking at economic cruising, you will have to do some calculation of speed/consumption to find the most economic speed. 16-17 knots is fine, and if you fancy 8 knots (Real ecospeed) do a fast run from time to time and engines are happy (I think )

 

[Latestarter1]

I have Volvo TAMD 61 A engines in a Fairline Turbo 36 and am trying to find the slowest economical planing speed
Book recommends 200 rpm below WOT revs. Max revs generally 2700 (I carry gear and half tanks min) which can give 27 kn but so 2500 giving about 23 kn is the recommended but this is a bit juicy on long runs
So.... Next most reasonable would be planning but with turbos just running
From the graphs in manual this would appear to be 2100 rpm
Am I correct in thinking
1. This value is correct
2. The turbos like to be running to prevent smoking and depositing oil and sooting up
These revs gives a speed of about 16 to 17 kn

Volvo guys will be along at some point however your understanding of turbocharger operation is incorrect.

#1 Your engines have a rated speed of 2,800 rpm not 2,700 rpm.

#2 Unless you can make rated rpm there is absolutely no point in trying to plot a boost curve, propellers move boats NOT engines, they simply respond to the demand placed on them by the propellers. Volvo tend to use a theoretical propeller exponent of 2.5, nothing wrong with that, however exponent is just that, theoretical, planing hulls can produce exponent in the range of 2.45 to 2.7.

#3 Not being a VP person and I may be wrong but 'Book recommends 200 rpm below WOT revs' suggests to me that 200 rpm off the top this is your highest continuous output rpm and not your most economical speed. IF you were propped correctly your maximum continuous output would be 2,600 rpm.

#4 Looking briefly at VP data sheets they only show full load consumption curve which tells you next to nothing.

I would suggest that you investigate why you are not making correct rated speed, ensure CAC's have been serviced. Once this has been done you can run trials and plot a boost curve at 100 rpm increments. Most VP 60 Series 2,800 rated engines have peak torque at 2,000 rpm, not sure where you are reading 2,100 rpm, however sweet spot is around this area.

Always remember that turbo boost is characteristic of engine loading and comments like 'turbos just running' are nonsense, they are running when engine is at low idle as some technicians have found out to their cost by losing finger tips.

Looks like 'Piratos' sneaked in with the same answer before I pressed send...............

 

[Rocksteadee]

Cheers guys, it's great when I get confirming answers

Trevor, I get about 1.2 at 16kn, could be to the different engines to your

The plate I am sure says "recommend" cruising speed. Max makes more sense
She will get to 2800 rpm, with a clean hull, no water on board, little fuel, no stores , no wind, a calm sea and if the missus jumps up and down. Then she is running just over 28 kn

Reading all 4 rev counter the same at 2000 rpm. Not checked with a tachometer
At 2000 it feels like a sweet spot as that gives me about 15 to 16 kn. depending on conditions and load quite (ish) and little vibration and feels comfortable

Most of the time I do 7 kn as best displacement speed with the occasional blast or short trips about 14 kn so now am happy to cruise at 2000 knowing the engines are running at their optimum

 

[superheat6k]

Cheers guys, it's great when I get confirming answers

Trevor, I get about 1.2 at 16kn, could be to the different engines to your

The plate I am sure says "recommend" cruising speed. Max makes more sense
She will get to 2800 rpm, with a clean hull, no water on board, little fuel, no stores , no wind, a calm sea and if the missus jumps up and down. Then she is running just over 28 kn

Reading all 4 rev counter the same at 2000 rpm. Not checked with a tachometer
At 2000 it feels like a sweet spot as that gives me about 15 to 16 kn. depending on conditions and load quite (ish) and little vibration and feels comfortable

Most of the time I do 7 kn as best displacement speed with the occasional blast or short trips about 14 kn so now am happy to cruise at 2000 knowing the engines are running at their optimum

Nothing wrong with slow crusing then an occasional faster cruise, but I like to 'let the engines breathe deeply' as the owners handbook for a BMW I once owned explained it, after a period of prolonged slow running - honest officer they were just breathing deeply (in that car that meant topside of 125 mph). Certainly blows the muck out of the turbos and injectors to occasionally open her right up in calm water for a couple of miles.