Beta engines again Yes I know it's been done to death.:-)

[Westerly Jetstream]

I have a Westerly Renown fin keeled ketch, and after catastrophic MD2B engine failure in western isles late last summer am replacing it with a Beta.
The issue I have is Beta recommend either the 3 cyl 30 or the 4 cyl 35. The 35 fits no problem and produces more power at much reduced revs, so will have lower vibrations and be quieter. We cruise am extended season in some heavy weather, so again I'm drawn to the 35.
IMHO the power and torque curve on the 35 is very attractive allowing a larger prop.
But I don't want to make a mistake it's only an extra 500 quid so no big deal ,but is it overkill?

 

[alahol2]

One point that is often made on here is that these engines prefer to be used at the upper end of their power curve. Too big an engine will be operating in its lower ranges and will suffer. But, the points you put in favour of the larger engine may outweigh this potential drawback.

 

[sailorman]

Go for the 35 it will be smoother,quieter.
i have a 37.5hp Nanni in a 7 ton boat,it is rated @ 3000rpm so less shaft rpm too & you can swing a coarser pitch to load the engine

I have a Westerly Renown fin keeled ketch, and after catastrophic MD2B engine failure in western isles late last summer am replacing it with a Beta.
The issue I have is Beta recommend either the 3 cyl 30 or the 4 cyl 35. The 35 fits no problem and produces more power at much reduced revs, so will have lower vibrations and be quieter. We cruise am extended season in some heavy weather, so again I'm drawn to the 35.
IMHO the power and torque curve on the 35 is very attractive allowing a larger prop.
But I don't want to make a mistake it's only an extra 500 quid so no big deal ,but is it overkill?

 

[Westerly Jetstream]

Agree but the lower revving 35 and bigger prop should mean i'm operating at rev point where torque and BHP cross. Which is 2200 max revs are 2800

 

[Westerly Jetstream]

Yep i'm swinging a bigger prop as recommended by Pete at first Marine Propulsion.

 

[macd]

Agree but the lower revving 35 and bigger prop should mean i'm operating at rev point where torque and BHP cross. Which is 2200 max revs are 2800

I'm not sure what you mean by this. The 'crossing point' of torque and power is simply an artefact of the units used. With imperial units it's 5252rpm; for kw/Nm it's 9549rpm. Neither has any intrinsic meaning. Nor, god willing, are either likely to be seen by your Beta. Good engines, by the way: good luck with it.

 

[Westerly Jetstream]

Very badly put by me sorry, Not crossing point. What I should have said was the RPM at which the Torque curve was at it's peak before it turned down again. On the 35 its as low as 2200 any further increase in revs although the BHP climbs to its peak at 35 the Torque drops off considerably.

 

[Bobobolinsky]

So..... What's the problem with that, it just means that you are only producing 28 Hp ish@2200 RPM

 

[Westerly Jetstream]

Absolutely No problem at all, I was quoting it as an advantage of the lower revving 35 over the 30, just trying to get the forums opinion on my choice.

 

[macd]

Very badly put by me sorry, Not crossing point. What I should have said was the RPM at which the Torque curve was at it's peak before it turned down again. On the 35 its as low as 2200 any further increase in revs although the BHP climbs to its peak at 35 the Torque drops off considerably.

No 'sorry' necessary. Looking at Beta's graph (which isn't v high-res), the 35's peak torque is around 93Nm at 2100rpm, dropping to maybe 84 at 2800rpm. That's not by any stretch of the imagination dropping off 'considerably'. The 30hp Beta delivers less torque and a peakier curve, (not that either is at all peaky), with a peak of 66Nm at 2600rpm.

You're quite right that the 35 would probably be smoother (the extra cylinder helps, of course) and 'lazier'. There are too many variables to make confident predictions, but setting up the 35's gearing/prop for a cruising speed near peak torque may well give the more relaxed set-up, with little or no penalty in fuel consumption. (Peak torque rpm is always where specific fuel consumption is lowest...but not necessarily the same as best mpg.) Although more frugal at lower revs, the 30's specific fuel consumption rises quite steeply towards the top end compared to the 35's. It's also 30kg lighter, which might be worth considering. I doubt that either engine will disappoint.

I believe that both engines now come standard with polyvee alternator belts: you'll love it. The one on my last boat went unadjusted, let alone changed, for 2000 hours.

 

[alteredoutlook]

i had the same dilemma when replacing my volvo 2003 28hp engine. I wanted the quieter running 35 but went for the 30 hp as this matched my existing prop - i didnt want the expense/hassle of buying a larger prop.

 

[ianj99]

So..... What's the problem with that, it just means that you are only producing 28 Hp ish@2200 RPM

In theory. In practice probably not actually using anywhere near this unless that's as high as it will rev due to the prop size restricting it.