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Old 20 May 2016, 02:55   #1
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2 stroke engine choice/weight/cylinders 25/30/40

I'm a bit in the dark regarding the larger 2 strokes - specifically 25, 30 and 40 hp.

Considering a new boat and the engine would likely be one of these sizes - can anyone explain the choices out there for say the last 15 years from Yam, Merc, Mariner? Not looking to buy older than this. The 40 would need to be PTT.

Do the 25 and 30 share the same block (weight?) - how many cylinders in each size - what sort of weight? Best specific models to aim for?

Cheers guys.
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Old 20 May 2016, 03:02   #2
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Do the 25 and 30 share the same block (weight?) - how many cylinders in each size - what sort of weight? Best specific models to aim for?
It depends! Some Yam 20/25 are the same block (2 cyl). Some Yam 25/30 are the same block. No 2str Yam 20 and 30 were the same block!
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Old 20 May 2016, 04:03   #3
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Max,

It's not a size I have complete understanding of but in my (paperwork not virtual) folder I have some info from when I looked at hard trailed boats and larger 2-strokes from early/mid 2000s.

Mercury... 25/30 near identical at 430cc 2-cyls 51kg. I think then the jump to 40hp was a 3cyl larger capacity 70kg lump.

Confusingly Mercury also did what's called a Sea Pro/Marathon you sometimes see advertised where the 30/40 are the same... a much more chunky motor at 644cc 2cyl which I think is 70kg+.

Tohatsu with the 25/30 being a 429 2cyl 51kg and the 40 jumping to a 697 3cyl 75kg.

As Poly says Yamaha are odd doing a 25 395 2cyl 50kg and also a 25/30 496 3cyl 60kg.

Thats about all I have noted in the file.

Anyway... what new boat would be OK with 25-40hp range... small RIB? RNLI thingy? Going trailed?
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Old 20 May 2016, 04:24   #4
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Anyway... what new boat would be OK with 25-40hp range... small RIB? RNLI thingy? Going trailed?
Cheers Poly, David.

Ahh, talking two boats not one.

Same old story, Y-Class or SR4 (for the 40).

Remind me again what your 4S 20 Suz' numbers are? - weight, WOT on the BAT, fuel, price...
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Old 20 May 2016, 05:58   #5
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Suzuki DF20A... 2300 or thereabouts... 44kg.

Not fully run in remember and only trialled at speed with a fair load and in choppy water for just a few seconds before backing off due to conditions.

Load... persons + dog = 532lbs then add all the kit and 20l fuel.

With a 10" prop it repeatedly climbed to 5750rpm and 19Kts in short sections and the only time I could keep the throttle wide open for 20sec I saw 20.5Kts without the rev limiter cutting in but it was far too rough to take my eye off the sea and look at the revs... I'd guess around 6000-6100rpm.

With your loads I reckon an 11" prop would suit better for another couple of knots.

But for me the impressive thing rather than flat out speed is being able to operate in the up to 19kt range without that lag after opening the throttle waiting for the boat speed to catch up which I've had with 10 & 15hp motors and our normal load.... it's much more instant.
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Old 20 May 2016, 06:22   #6
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Is the 20 the biggest on that block?
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Old 20 May 2016, 06:28   #7
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Yes... Jeff has the 25 version on his trailed setup. Extra cylinder, 30% extra capacity, another 550 and weighs 62kg.
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Old 20 May 2016, 07:49   #8
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Mariner 25 is a 2 pot (same as Yamaha?) the larger are 3 pot so heavier.

Saw some very deft handling of Yamaha 40 tillers (manual trim and tilt) on the beach this week in Portugal by the watersports guys.
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Old 20 May 2016, 11:47   #9
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Cheers.

Anyone got more on the 40's - Yam? Are they mostly 2 cylinder.

What's the advantage with a 3 cyl 40 over the 2 cyl 40? More grunt/holeshot? Less stressed?
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Old 20 May 2016, 13:43   #10
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Max

Go on Ron hale marine site you can compare yam, suzi,merc, tohatsu ,Honda are larger engines than you want it gives all the points gizmos all the weights long short shaft.

Cheers
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