Volvo Penta TAMD31L OVER PROPPED?

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Brufen600

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I. First of all sorry for my english. I am portuguese so english is far from native.

I recently bought a Rodman 700 from 1994 with 7m (23ft) for 2.81m (9ft) and +/-2000kg of weight with a Volvo Penta TAMD31L 130HP shaft drive transmission.
In the process of restoration and improvments i needed to buy a new proppeler so i ask a manufacture to make me a copy from the original (the previous owner told me that never changed proppeler).

With the brand new proppeler i manage to do full throttle 16Knots @3400 RPM

Now FACTS:
- Volvo says this engine should do 3800RPM. Considering the engine is 26 years old but sounds quite healthy (3500 hours but well cared), is it normal that i can't get the 3800RPM???
The exhaust steams a little over 3000rpm but i think it's normal by the turbo usage right?
- In neutral i can reach 4400 RPM. Is it normal considering that the specs of the engine says 3800rpm??

Shure i'll find here some experienced guys and techs that can give me some piece of advice. I don't want at all to be pushing the engine too much.

Thank you very much for your attention

Pedro
 
I take it the hull is clean? Sounds over propped if that is the case. It is worth asking Rodman what prop they fitted I would think.
 
gordmac said:
I take it the hull is clean? Sounds over propped if that is the case. It is worth asking Rodman what prop they fitted I would think.
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"With the brand new proppeler i manage to do full throttle 16Knots @3400 RPM" (HULL CLEAN, 11/09/2020), sorry, forgot to add this info
 
I would think that level of power won't give much speed anyway. Well worth a chat with Rodman or their Portuguese importers.
 
gordmac said:
I would think that level of power won't give much speed anyway. Well worth a chat with Rodman or their Portuguese importers.
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I'm on it, trying to contact them, waiting for answers.
I'm not expecting more speed. I would be happy with 12knots cruising and 16knots of max speed. I'm just worried that i'm overloading the engine.

I'm thinking maybe if by reducing a little the prop i manage to increase a little bit the rev's and not necessarly increase the fuel consumption because probably i wouldn't push the throttle so hard. Does this make sense?
 
Brufen600 said:
I'm thinking maybe if by reducing a little the prop i manage to increase a little bit the rev's and not necessarly increase the fuel consumption because probably i wouldn't push the throttle so hard. Does this make sense?
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Yes - fuel burn is proportional to load, not so much engine speed. It is important to make sure the boat engine can reach its max rpm when clean as this means the engine is operating at its best. Otherwise it will be working too hard at too low a rpm and the various cooling effects are not as good - hence trouble.
It does sound like the boat is over-proped assuming the hull and prop is very very clean.
 
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