Replacing with Rebuild used marine engine

[Tranona]

Not a good idea. You need 35hp to get hull speed, so the range of engines suitable are the ones already discussed Beta 3/8 Yanmar 3JH40, Volvo D2 40 Vetus M4 35 or maybe 45 The 30hp are obviously physically smaller. It is displacement that counts and a 30hp is OK up to about 6 tonnes (my boat is 5.4tonnes with a Beta 30) but yours is 7 tonnes. Hence the fitment of the 2003T when new. As I suggested earlier the Yanmar is probably the best compromise if space does prove to be an issue otherwise a Beta 38 is a good choice for 4 cylinder engines.

 

[Nina Lucia]

Not a good idea. You need 35hp to get hull speed, so the range of engines suitable are the ones already discussed Beta 3/8 Yanmar 3JH40, Volvo D2 40 Vetus M4 35 or maybe 45 The 30hp are obviously physically smaller. It is displacement that counts and a 30hp is OK up to about 6 tonnes (my boat is 5.4tonnes with a Beta 30) but yours is 7 tonnes. Hence the fitment of the 2003T when new. As I suggested earlier the Yanmar is probably the best compromise if space does prove to be an issue otherwise a Beta 38 is a good choice for 4 cylinder engines.

Thank you

 

[Refueler]

Someone suggested downsizing the engine from the Volvo Penta 2003T 43HP to Yanmar 3YM30AE 29HP. Will those be good options?
Thank you

My 5 ton 38ft Conqubin has a Yanmar 2GM (20HP) ... on a two blade folder ... no problem - she motors nice ... I expected to have to use quite high revs - but in fact not.
OK - I don't have some of the tide streams / currents that some harbour entrances have in UK - but I'm still happy with it. She's motored though some pretty tough rough seas without any problem.

 

[Nina Lucia]

I found exactly the same boat for sale in Sweden with a Yanmar 3YM30AE that they replaced their original VP2003T. I wonder what they think about performance?

 

[Tranona]

My 5 ton 38ft Conqubin has a Yanmar 2GM (20HP) ... on a two blade folder ... no problem - she motors nice ... I expected to have to use quite high revs - but in fact not.
OK - I don't have some of the tide streams / currents that some harbour entrances have in UK - but I'm still happy with it. She's motored though some pretty tough rough seas without any problem.

But your boat is a 5 tonne cruiser racer not a 7 tonne heavy cruiser! Much better to do the sums with the actual boat data to determine what is required and what performance you can expect.

 

[Refueler]

But your boat is a 5 tonne cruiser racer not a 7 tonne heavy cruiser! Much better to do the sums with the actual boat data to determine what is required and what performance you can expect.

Maybe its WHY I put the weight / boat brand ??

Of course I could have expanded on the 4-107 in my other boat .. a 4tonne 25ft Motor sailer ... that 4-107 is one of the 43HP versions - according to serial number was originally produced for static engine work.

 

[Tranona]

I found exactly the same boat for sale in Sweden with a Yanmar 3YM30AE that they replaced their original VP2003T. I wonder what they think about performance?

It depends on what they want. They will get the performance the calculations give them which is a top speed of 7.02 knots against a hull speed of 7.34knots. Unsurprising given the calculations show approx 35hp required for hull speed. I did the sums for the 3JH and that will give you 7.84 knots - 0.4 knots over rather than a similar amount under. Why does it matter when you are unlikely to ever use full speed? Manufacturers recommend running at half engine power and 65-70% revs for cruising. If you look at the power curves this is usually peak torque and lowest specific fuel consumption. In practical terms this means cruising revs between 2-2200 for 5.5-6knots. With the smaller engine this jumps to 2500-2700 with higher noise levels. You also lose much of the reserve power for use in adverse conditions and punching tides. There is little or no fuel penalty using the larger engine as consumption is a function of the power you use not what the engine is capable of producing.

I had this sort of choice with my last boat a Bavaria 33 at 5.5 tonnes. Standard engine is 20hp, too small for hull speed, but for £1k more there is a 30hp option. The lower hp was sort of OK for charter use in benign places like the Ionian, but just about every UK buyer like me specified the larger engine option for the greater reserve and more relaxed cruising. Similar with my current GH31. 27hp required for hull speed so chose the Beta 30 rather than the 25 (the original was a Lister 20 - way under although somebody had replaced it with a Perkins 35 which was way over!)

Najad would have had a similar dilemma when new. The previous Volvo range had the MD17 at 36hp - big old lump, The 200X range only went up to 39 and the next size up was 50hp, hence turbocharging the 2003 to fill that gap which HR and the others also needed for their new 35-38' boats. Not their best effort but did the job until the Perkins based range came in with a proper 40hp engine.

Sorry for the long explanation but it is my view that if you are going to put a new engine in a quality boat like yours do the same as the builder would do, fit one that is on the larger side without being excessive. The incremental cost is small in relation to the benefits, particularly the more refined cruising while staying in the ideal rev range.

 

[Tranona]

Maybe its WHY I put the weight / boat brand ??

Of course I could have expanded on the 4-107 in my other boat .. a 4tonne 25ft Motor sailer ... that 4-107 is one of the 43HP versions - according to serial number was originally produced for static engine work.

So neither of your boats helps the OP, One is grossly overpowered and the other under. Outcomes are predictable and illustrate what should be avoided.

 

[Nina Lucia]

Not a good idea. You need 35hp to get hull speed, so the range of engines suitable are the ones already discussed Beta 3/8 Yanmar 3JH40, Volvo D2 40 Vetus M4 35 or maybe 45 The 30hp are obviously physically smaller. It is displacement that counts and a 30hp is OK up to about 6 tonnes (my boat is 5.4tonnes with a Beta 30) but yours is 7 tonnes. Hence the fitment of the 2003T when new. As I suggested earlier the Yanmar is probably the best compromise if space does prove to be an issue otherwise a Beta 38 is a good choice for 4 cylinder engines.

Yes, she is 7.2 tonnes

 

[Nina Lucia]

It depends on what they want. They will get the performance the calculations give them which is a top speed of 7.02 knots against a hull speed of 7.34knots. Unsurprising given the calculations show approx 35hp required for hull speed. I did the sums for the 3JH and that will give you 7.84 knots - 0.4 knots over rather than a similar amount under. Why does it matter when you are unlikely to ever use full speed? Manufacturers recommend running at half engine power and 65-70% revs for cruising. If you look at the power curves this is usually peak torque and lowest specific fuel consumption. In practical terms this means cruising revs between 2-2200 for 5.5-6knots. With the smaller engine this jumps to 2500-2700 with higher noise levels. You also lose much of the reserve power for use in adverse conditions and punching tides. There is little or no fuel penalty using the larger engine as consumption is a function of the power you use not what the engine is capable of producing.

I had this sort of choice with my last boat a Bavaria 33 at 5.5 tonnes. Standard engine is 20hp, too small for hull speed, but for £1k more there is a 30hp option. The lower hp was sort of OK for charter use in benign places like the Ionian, but just about every UK buyer like me specified the larger engine option for the greater reserve and more relaxed cruising. Similar with my current GH31. 27hp required for hull speed so chose the Beta 30 rather than the 25 (the original was a Lister 20 - way under although somebody had replaced it with a Perkins 35 which was way over!)

Najad would have had a similar dilemma when new. The previous Volvo range had the MD17 at 36hp - big old lump, The 200X range only went up to 39 and the next size up was 50hp, hence turbocharging the 2003 to fill that gap which HR and the others also needed for their new 35-38' boats. Not their best effort but did the job until the Perkins based range came in with a proper 40hp engine.

Sorry for the long explanation but it is my view that if you are going to put a new engine in a quality boat like yours do the same as the builder would do, fit one that is on the larger side without being excessive. The incremental cost is small in relation to the benefits, particularly the more refined cruising while staying in the ideal rev range

 

[Nina Lucia]

Thank you so much, well explained and understood!

 

[Refueler]

Seems many here have forgotten what it was like years ago .... with the Vires ... Listers .... Stuart Turners etc .... some large heavy boats had some ridiculously small engines ... but they worked and survived ...
If you were bound for a harbour such as Portsmouth / Langstone etc - with the high flow rates IN / OUT .. then you timed your transit to have quietest period.

No doubt someone will now take me to task on this now !

I would not be so adamant about fuel consumption changing little between engine sizes to produce same speed etc. Fuel consumption is not only based on RPM - but also on how many cylinders the engine has ... think about it .... a 2cyl engine idling will burn significantly less fuel than a 4cyl idling ... now increase the revs ... I agree that the smaller engine will need to rev higher to match speed of the larger and consumption will suffer .. but the larger engine will still usually burn more fuel ....

Another opportunity to take me to task !