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Ispearem
09-08-2012, 08:05 PM
hi all,

I have a UB520. Currently I run it with a 90Hp Yammy 2 stroke. It gets along nicely. I am thinking of changing to a 4 stroke to get more economy. I like yammys but the 80 Yammy 4 stroke is around 60kgs heavier then the 90 2 stroke. I am pretty sure the 70 Yam 4 stroke is the same weight as the 90 2 stroke, but obviously with 20 less Hp.

I am wondering whether the weight will affect the performance of the boat, and / or if the 70 Hp 4 stroke will be lacking power? I am unlikely to have more then 3 people on board, and often carry camping gear which can add up.

Has anyone done this with a UB520 ? If so, what did you find?

cheers

White Pointer
09-08-2012, 08:26 PM
G'day,

I might be having a memory lapse but I can't remember what a "UB520" is. Does the boat have an ABP - a plate close to the helm that sets our weights and power limitations?

Regards,

White Pointer

Dan5
09-08-2012, 08:31 PM
A UB520 is a longboat...........proberbly one of the only hull designs that would handle down powering well.
It should be capable of the 80 yammie all the same.

Dan

Moonlighter
09-08-2012, 08:55 PM
It would be worth checking out the new lightweight Suzuki 90 4stroke. Would be a great match I think on that boat. 155kg just 30 kg more than the old Yammy 90. Would use half the fuel.

Cheers

ML

Noelm
10-08-2012, 09:05 AM
the Suzuki 90 is the lightest 4 stroke in that HP by heaps, I guess the others will bring out lighter and lighter models in the coming years, I think going down in HP, but up in weight, is going to leave you disappointed.

Andy56
10-08-2012, 09:37 AM
I too think you will be disapointed. A 90hp carbie 2stroke equivalent would be a 115hp 4 stroke, performance wise. (they are getting closer every year, lol) A better fit would be an etec 90 or merc equivalent. Then you can have the power and economy.
It's not a 4stroke vs 2stroke thing, both are good, but just on what info you have provided, I think these would be a better fit. But if you go 115hp, then the Suzy would be a good fit and etec even better. Not an easy decision I know

Noelm
10-08-2012, 09:54 AM
not too sure that is 100% correct, all motors have their HP measured at the prop, and up to a point, a 4 stroke has a lot better "usable" power down low, so unless you want to floor it everytime you take off, then a 4 stroke will achieve a nice smooth plane a lot easier than a 2 stroke (in my opinion)

MTAQ/BTAQ
10-08-2012, 10:03 AM
I have a 6.2M Dolphin Flexihull Longboat, the plastic version, (it does boat licensing) - I switched from a 70 HP 2 stroke Yamaha (70HP is the maximum HP for this boat) which weighed 108kg to a 70HP 4 stroke Suzuki which weighed 152kg in 2007. There was little difference in affect on the vessel, slightly lower in the stern (it has a cut away transom) at rest but quieter, no smell and very economical which are essential ingredients in my business.

bigmac87
10-08-2012, 10:06 AM
I recon the 90 etec would be the go. A mate did a swap on his old 75 2 stroke merc for a 75 etec for the same reason. he has never looked back since. great punch and good econ he says.

NoBananas
13-01-2013, 07:56 PM
Ispearem,

Did you have any luck on the motor change? I have the same boat I'm keen a 4 stroke, I also have a 90Hp 2 stroke Yam.

Cheers

NoBananas
13-01-2013, 07:58 PM
What size pitch/prop are you using on the 90?