Repowered 5.2 KC with twin 60 suzuki's.

[Danf]

I am thinking about a set of 4 strokes on my 5.2 tournament. I have xl 70 hp yamis at the moment. Anyone ever considered the Mercury 60 4 strokes?

[finding_time]

WOT at 6300 sounds a bit excessive to me- suprised no one has mentioned it. Perhaps it is ok for this motor but I was always of the opinion that a correctly proped 4 stroke would rev between 5800 and 6000 at WOT. I would also expect a cruise speed in the low 20s and at revs of around 4200.
I would be inclined to at least try out a 15" pitch and would imagine you might improve your top end a bit, I would have thought a 5.2 Kevcat with twin 60s should be able to achieve closer to 35kn. Doubt there would be any noticeable decline in holeshot with a 15- only one way to find out.
Also- not sure if it just the photos, but the motors seem to be very low. does the cav plate draw about level with the bottom of the hull? They look to be well below which may hinder your performance, as I said, could just be the angle of the photo.

Cheers,

Cam

Mate there wont be a 5.2 kc with 60's that can get 35 knots they tend to top out at 31 knots if the engines are at the right height, there proped correctally and travelling slightly down wind

Cruise speed of around 22 knots should be at around 4800.

I too think 6300 is abit much although the susuki's are supposed to rev higher! If he was getting to that rpm , one up and with hardly any load onboard( fuel, ice etc) i would say he was near spot on. But atm he's probably not got enough prop.

From memory the cav plate on the engine wants to be 2 and 1/4 inches above the bottom of the hull but Dean will confirm this!


Ian

[Chris20984]

try a set of 4 blade;s

I remember reading that someone else with 60 yamies spent a lot of time trialing all sorts of props from solas, including 4 blade's and they ended up settling the original 15 ' Yamaha props on. Not sure if this would be the same for the zukes ???

Nothing ventured, nothing gained ! Cheers Chris

[Chris20984]

It might be worth paying the money and getting Solas to come out and try a range of props to get maximum benefit. Pretty good motors the 60 Suzuki hey! very light, nice sound and great fuel economy.

Dose anyone know roughly how much it costs to have someone from solas trial different props ? I am going to get some accurate fuel usage figures running the 14's and then the 15's, and then i will try the solas option.

Love the new motors, quiet, powerful, fast. just need to do a bit of fine tuning yet.

[Chris20984]

yes a grunty little 60 the new Zuke, from a few comparo's ive seen they out perform the Yam 60 and very close to the Yam 70 apparently

Hope so, only time and testing will tell.

[Chris20984]

yep, I reckon you would be right there, they are a nice engine, have you noticed how soft the engine mounts are on the Suzukies? kind of scares me a bit, they are so springy, compared to (say) a Merc or other brand, after the 90HP they are reasonably hard though.

I too was very surprised at how softly they are mounted, they seem very still while cruising along though.

[Chris20984]

WOT at 6300 sounds a bit excessive to me- suprised no one has mentioned it. Perhaps it is ok for this motor but I was always of the opinion that a correctly proped 4 stroke would rev between 5800 and 6000 at WOT. I would also expect a cruise speed in the low 20s and at revs of around 4200.
I would be inclined to at least try out a 15" pitch and would imagine you might improve your top end a bit, I would have thought a 5.2 Kevcat with twin 60s should be able to achieve closer to 35kn. Doubt there would be any noticeable decline in holeshot with a 15- only one way to find out.
Also- not sure if it just the photos, but the motors seem to be very low. does the cav plate draw about level with the bottom of the hull? They look to be well below which may hinder your performance, as I said, could just be the angle of the photo.

Cheers,

6300 is hitting the rev-limiter, and this is with a medium load, half fuel, 3 blokes and safety gear.

Apparently these 60's are quite happy to sit on 5000 rpm for hrs, which brings me to the question that is it better to have a motor reving to 5000 that is not struggling with the torque, or a motor reving at 4600 that is working harder ? It is not ideal to have a four stroke reving too high ( unless it is made to handle it) and it is not ideal to have a four stroke laboring too much. ??? Ultimately i think fuel consumption will be the deciding factor in 14 vs 15 ' prop.

I would love to know how to set up a KC 2x60 hp to achieve 35 kn. not sure it is possible, yet !

The height of the motors is pretty close to the figures proven by other KC owners, 2 and 3/4 from hull. I will take some side on pics and do some measurements. The photo is a bit misleading.

Cheers Chris.

[Chris20984]

yes exactly, you will be better off getting your engine height spot on before exchanging props, there will be some experienced with KC5.2's on here but i bet you will almost get away with having the cav plates level with the bottom of the pods. you should be getting a nice clean wake at planning speeds with minimal sprinkler water coming off the engines, or walk down the back and see where your cav plates are sitting while on the plane. if you are hitting 6300rpm with fuel and 3 blokes and your engines are too low then you will find that it will spin the next pitch prop easily and maybe even more, by the way you described the handling the enginesare probably too low, you will be surpirsed by how much difference it can make.

There is a nice clean wake whilst planing, I can easily see the cav plate just on top of the water, i will take some pics of it in action so you can see if i am on the right track.

Thanks for all the input everyone

[Dean1]

Yes 2 3/4 inches from bottom of hull to cav plate is correct. Dont bother with 4 blade props on 60's you will be dissapointed. Make sure the height is right before anything as i gained 3 kts and 400 rpm by raising mine one hole to the right height.

Ive been thinking about doing what Ian did and taking some meat off my 15's to get better performance when fully loaded etc.

Have thought about the solas experiment as well as ive been told the original yammie props arent much chop Well solas tell me they arent a very good design.

Spinning yours to 6300 so quickly and easily makes me think a 15 will be a better alternative. Gee you may get over 30kts and a better cruise speed/revs.

good stuff, Deano.

[Danf]

Yes 2 3/4 inches from bottom of hull to cav plate is correct. Dont bother with 4 blade props on 60's you will be dissapointed. Make sure the height is right before anything as i gained 3 kts and 400 rpm by raising mine one hole to the right height.

Ive been thinking about doing what Ian did and taking some meat off my 15's to get better performance when fully loaded etc.

Have thought about the solas experiment as well as ive been told the original yammie props arent much chop Well solas tell me they arent a very good design.

Spinning yours to 6300 so quickly and easily makes me think a 15 will be a better alternative. Gee you may get over 30kts and a better cruise speed/revs.

good stuff, Deano.

Would that height be at the maximum before the propellers suffered any breakout, like when in quartering seas? Would you need more cupping on the props?

[Noelm]

motors can be run very high if extreme performance is the main aim, on a fishing/pleasure boat, a compromise is needed, so high running on the limit is not what you are after, you want good performace everywhere, not just at WOT on a glassed out lake. Kind of interesting that the motors appear to be not moving too much when running, those soft mounts sort of seem like it would be jumping about.

[Smithy]

Cupping will give you something like an extra 200rpm. That is all it is for. I get a lot less trim range with my 150 than my 140. So long as you can trim to level and a bit more before you start to get cavitation that is fine. Like everyone else has said you will probably pick up a few hundred rpm lifting if you can.

[trueblue]

different boat, but I lost 200 rpm by cupping a 4 blade prop.........

made it grip the water beautifully, but now I need to get the prop blades trimmed back (ground down in diameter size, but retaining cupping) to get the rpm back.......

[Danf]

different boat, but I lost 200 rpm by cupping a 4 blade prop.........

made it grip the water beautifully, but now I need to get the prop blades trimmed back (ground down in diameter size, but retaining cupping) to get the rpm back.......

That's what normally happened when we used to cup our own props, back in the 80's, when we had a lot of time on our hands.

[Noelm]

cupping will usually reduce RPM, it also allows a motor to run a lot higher, and helps reduce some slip, it in effect directs more water towards the rear to increase thrust.