Best engine for swan 47
dear Lars
I have Hull # 041 Tortuga, she is the NYYC version shorter mast and longer boom.
Dispiacement Is around 17 tons.

My engine Is too large volvo mb 31 with 100 horse power and it has many issues.

What do you think about Nanni 50 horse power it has high displacement 2100, low rev 2800 and no turbo.
It Is enough? Or there Is a turbo version at 1,9 dispiacement with 60 horse power.

Alternatives are volvo d2 75hp or yanmar 75. or Nanni 87 that seems too Big.
Perkins i need to investigate.

Regards
Filippo

Dear Filippo
Thank you for bringing up an interesting subject.
Usually engine power is determined on the basis of hp per ton of weight, and the recommendations keep increasing.
It is assumed that you normally cruise below 8 knots, and then little engine power is needed in calm weather, pls see the appended curve.
When there is a strong wind on the nose the engine power becomes important. One way to estimate the ability to proceed against the wind is to calculate the bollard pull, i.e. the propeller thrust when the yacht is held stationary. Here the engine, reduction ratio, and propeller characteristics play a big role.
The wind speed causing a wind resistance equal to the bollard pull can then be determined, and is a measure of the yacht's ability.
It is also possible to measure the bollard pull with a dynamometer.

As an exercise I could do a bollard pull and wind speed calculation for your yacht with for example the 50 hp Nanni. If you have a Max-Prop and will keep it the number of blades and the diameter are required.
Kind regards
Lars

Would recommend looking at Beta as well. From memory the 50HP and 60HP use the same kubuto block as the Nanni engines of the same HP, but when we re-engines a few years ago was much cheaper.

I will be interested to see what you go for, as we deliberated over the 50-60 for some time; even though the 50 is able for our 44. Came down to price and matching optimal engine load against normal cruising speed.

Some observations referring to Beta and Nanni engines.
The Beta engine leaflets give the manufacturer's maximum power, as well as the power for pleasure craft applications according to ISO 8665. The latter is the available shaft power, and it can be noted that for Beta 60 the available SHP is 47 hp, and for the Beta 50 it is 45 hp.
It appears that Nanni does not specify the power according to ISO 8665, and without this proper calculations can not be done.
Kind regards
Lars

dear Lars I have Hull # 041 Tortuga, she is the NYYC version shorter mast and longer boom. Dispiacement Is around 17 tons. My engine Is too large volvo mb 31 with 100 horse power and it has many issues. What do you think about Nanni 50 horse power it has high displacement 2100, low rev 2800 and no turbo. It Is enough? Or there Is a turbo version at 1,9 dispiacement with 60 horse power. Alternatives are volvo d2 75hp or yanmar 75. or Nanni 87 that seems too Big. Perkins i need to investigate. Regards Filippo

Dear Professor,
Thank you very much for your replay, My max prop Is 3 badessa and has a radius of 260 cm. I am now looking at volvo/yanmar 75hp or Nanni 50 no turbo or 84 HP.

The original engine was perkins/volvo 62 HP but nowdays everybody has remoto reed with l'arteria engine. I am quote happy cruising at 6/7 knoots and not any fastweb than that.

Regards
Filippo

dear Lars I have Hull # 041 Tortuga, she is the NYYC version shorter mast and longer boom. Dispiacement Is around 17 tons. My engine Is too large volvo mb 31 with 100 horse power and it has many issues. What do you think about Nanni 50 horse power it has high displacement 2100, low rev 2800 and no turbo. It Is enough? Or there Is a turbo version at 1,9 dispiacement with 60 horse power. Alternatives are volvo d2 75hp or yanmar 75. or Nanni 87 that seems too Big. Perkins i need to investigate. Regards Filippo

Dear professor,
My max prop Is 3 Blazers 20 inchieste or 520 cm diametro
Regards
Filippo masci

Some observations referring to Beta and Nanni engines. The Beta engine leaflets give the manufacturer's maximum power, as well as the power for pleasure craft applications according to ISO 8665. The latter is the available shaft power, and it can be noted that for Beta 60 the available SHP is 47 hp, and for the Beta 50 it is 45 hp. It appears that Nanni does not specify the power according to ISO 8665, and without this proper calculations can not be done. Kind regards Lars

Dear Lars
Would it be possible to have the calculation on volvo d2 75 hp?
My propeller is a 3 blade max prop diameter cm520 or 20 inch
Kind regards
Filippo

Dear Filippo
Referring to powering against the wind, calculations show that with Volvo D2-75 at full power and your present Max-Prop the maximum wind speed would be about 50 knots in smooth water.
A propeller chosen for providing high thrust in this condition could increase the maximum wind speed by over 20%.
On the other hand the engine load when cruising should be at least 25% of the maximum power, i.e. 18 hp for this engine, and if you look at the speed-hp diagram provided earlier this means that the minimum cruising speed is a little over 7 knots.
Would you have further questions?
Kind regards
Lars