Is 260hp enough........

ST840

ST840

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For a 4.5 tonne planning single engine boat with duoprop leg?
This question was asked of me when a discussion about a potential boat was started.
I'm guessing yes, but is there a weight to HP guide manufacturers use. I ask because you see a few boats with different engine power options, but I can't find any info on this particular boat to give me an answer!
 
IMO no, but depends what you want to do [or what else is available].
My boat fits that spec and when we put in new ponies, it was 300 min and 350 is perfect.

If you want a good cruising load you'll be flogging those nags all day long, which wont be good.

No matter what the gallery here thinks, old engineering is never as efficient as new, and even though it says 260 on the badge. depending on age you will also be looking at losses.
 
Depends what you want out of the boat, I'm sure it would plane lightly loaded, but it wouldn't be fast and it wouldn't take much to stop it being able to plane.

My boat, 2.5 tons, with 260hp and duoprop is fine,and will do 42 knots when clean, lightly loaded. But another 2 tons would affect that a lot.
 
I have a 3.5 ton 1968 Bertram 35 with a single 320hp diesel on a Bravo 2 (so not duoprop). The gearing and prop are wrong but she'll do 25 knots flat out as is. I could get her to 28-30 by changing prop or gear ratios.

Seems a bit on the low side does 260hp

Edit - 25 not 35!
 
Last edited:
jointventureII said:
I have a 3.5 ton 1968 Bertram 35 with a single 320hp diesel on a Bravo 2 (so not duoprop). The gearing and prop are wrong but she'll do 25 knots flat out as is. I could get her to 28-30 by changing prop or gear ratios.

Seems a bit on the low side does 260hp
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My current boat is a smidge under 4 tonne @ 28ft and with a 260hp single shaft, she maxes out at 24knts. So cruising at 20knts for me is just fine. Am I right in thinking that due to duoprop and gearing the 260hp on an outdrive will perform better than a shaft? If so, then add a bit of extra weight and I should be able to achieve similar if not slightly better performance?
 
ST840 said:
My current boat is a smidge under 4 tonne @ 28ft and with a 260hp single shaft, she maxes out at 24knts. So cruising at 20knts for me is just fine. Am I right in thinking that due to duoprop and gearing the 260hp on an outdrive will perform better than a shaft? If so, then add a bit of extra weight and I should be able to achieve similar if not slightly better performance?
Click to expand...

Stern drives are much more efficient than shaft, so you should see similar performance IMHO. I have 300hp in a similar weight boat, but spread over two engines (sterndrives with duoprops). The extra drag etc of the second drive train probably means I would get very similar results with a singe of 260hp. I max out at 30 knots and cruise at 22.
 
madabouttheboat said:
Stern drives are much more efficient than shaft, so you should see similar performance IMHO. I have 300hp in a similar weight boat, but spread over two engines (sterndrives with duoprops). The extra drag etc of the second drive train probably means I would get very similar results with a singe of 260hp. I max out at 30 knots and cruise at 22.
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That sounds more like exceptable figures.
 
ST840 said:
My current boat is a smidge under 4 tonne @ 28ft and with a 260hp single shaft, she maxes out at 24knts. So cruising at 20knts for me is just fine. Am I right in thinking that due to duoprop and gearing the 260hp on an outdrive will perform better than a shaft? If so, then add a bit of extra weight and I should be able to achieve similar if not slightly better performance?
Click to expand...

The gearing can be altered but as mentioned, the drag is quite a bit less.

My boat is 25ft not 35, I've edited my post since.

Be careful over about 300hp diesel on sterndrive, not all of them can deal with the torque
 
Have you asked the broker? Would it not be worth going over there for a look and a sea trial? Perhaps even ask them to video revs and speed for you? Any information on how seaworthy the hull design is? From memory is it not a very rare boat? There might be a reason for that.
 
gordmac said:
Have you asked the broker? Would it not be worth going over there for a look and a sea trial? Perhaps even ask them to video revs and speed for you? Any information on how seaworthy the hull design is? From memory is it not a very rare boat? There might be a reason for that.
Click to expand...
The seller has provided performance figures of 30knt max with a usual cruise of 15-20knt.
 
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