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salt rat
24-02-2009, 11:29 PM
Thinking of replacing my 95 model 115hp 2 stroke yamaha with a 05 model 115 4 stroke yamaha. The extra 20 odd kg is not a problem but am worried about preformance. The hull is a 95 sportfish cuddy 5.5m and max hp rating is 115hp.
Is any one running this set up and if so how does it work ?

Thanks in advance cheers craigo.

ozbee
25-02-2009, 03:24 PM
will seem a bit gutless on hole shot but will get there also quiet with half the fuel use

roydsy
25-02-2009, 03:31 PM
Having the right pitch prop will make all the difference.

Malcolm W
25-02-2009, 05:54 PM
The 115 2 stroke is a detuned 130 that reaches 115hp at a fairly low 5000 rpm as opposed to the 115 four stroke 115hp at 5500 rpm. The 2 stroke is a strong motor with plenty of torque for heavy loads. I have the 2 stroke on my 5.6 ali and recently hired a similar boat on holidays but with the 4 stroke yamaha. When I took it out with 2 people it flew. Went back to the ramp and picked up 4 more, a big full esky and it was unable to get the boat up on the plane and rev out. I was suprised at the lack of grunt/ torque compared to my 2 stroke. Nice and quiet and no smell. I recently went through changing props on my 2 stroke and when I rang solas the first thing they asked was is it a 2 or 4 as the 4 wont push a 4 blade prop. If the current motor is just enough to power your boat you may be dissapointed with the 4 stroke. Not a 4 stoke knocker as I would prefer to have one on my boat with the same power and 4 stroke advantages.

Wahoo
25-02-2009, 07:53 PM
I recently went through changing props on my 2 stroke and when I rang solas the first thing they asked was is it a 2 or 4 as the 4 wont push a 4 blade prop.


is this really what the guys at solas said??

dfox
25-02-2009, 08:14 PM
My mate has the same rig (5.5 sportfish) but in a center console, its used commercially and is powered by a 100 yam 4 stroke (17p yammy ss prop). Considering the loads ive had with him on it. I'd be happy with the setup your thinking of, go ahead and change ... foxy

finding_time
25-02-2009, 08:30 PM
I took it out with 2 people it flew. Went back to the ramp and picked up 4 more, a big full esky and it was unable to get the boat up on the plane and rev out. I was suprised at the lack of grunt/ torque compared to my 2 stroke. .


This isn't a motor issue it's a prop issue ! As far as revs go that just a differance in motor types , a four stroke should rev to 5800-6000 and a 2 stroke will rev lower there differant and cannot be compared by rpm

Ian

FNQCairns
25-02-2009, 08:52 PM
It will be down like 25% in overall grunt, the extending of the rpm rubber band into 6000+ means the 4 can use gearing/ lower pitch easier to push props and give enough trust to perform well enough.

On most small fishing boats more often than not it's the wind speed/wave size for the hull ability that governs the average speed of the boat over any 10 trips, not the engine size.

If you ever want to set the 4 up to just go silly for speed or tow 2 skiers fast or carry heavy loads to a remote island/whatever, then the 4 will pail in comparison to the 2, no matter what the prop.

cheers fnq

Malcolm W
25-02-2009, 09:40 PM
is this really what the guys at solas said??

Yes, I was a little suprised as I had considered at one stage to change to the 4 banger ( mainly to increase my range) and solas said the 4 stoke did not have the grunt, or was suited to push a 4 blader on a 5.6m boat. That does not mean they did not have a suitable prop for it. I am not saying this is right as I just took their advice.

Wahoo
26-02-2009, 06:10 AM
thanks Mal,
i understand what your saying, you went to a prop guy asking for advice, all i can say is this is very poor advice from solas, i wonder if this guy is still working there, as this is the biggest load of crap i have herd for a while, i would of walked out of there shaking my head, there are 4 blade props that will suit you outfit very well, just have to talk to a few PPL that REALLY know whats going on