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60 or 70 hp

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    Posted: 20 Jun 2019 at 8:25pm
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Hey guys looking at repowering my 4.8m kiwi kraft at the moment it's a bit ass heavy with a Honda 90hp. so im looking at upgrading to either a 60hp Honda, suzuki, Mercury, yamaha or the 70hp yamaha anyone run one these motors on a similar sized boat? What sort of cruising/topspeed do you get and what sort of economy? For those of you running 60hp do you feel underpowered? I do a lot of beach launching/bar crossing.
Cheers troy
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Post Options Post Options   Likes (0) Likes(0)   Quote Joker Quote  Post ReplyReply Direct Link To This Post Posted: 21 Jun 2019 at 8:48am
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I had a 60hp 4-stroke Mercury on a FC500 CC that performed very well. I did go for a 4 blade prop for the extra lift, thrust and economy on the plane - I believe that this made a big difference. Now I would go for the Mercury Command thrust for the same reasons. Top speed with 2 medium size crew was 35mph with a 23mph cruise speed for around 11lph. Game fish trolling speed used 5.2lph.
A comparison with a similar sized boat with 60hp mercury 3 blade on the same trip used 20% more fuel.
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Post Options Post Options   Likes (0) Likes(0)   Quote Polar_Kiwis Quote  Post ReplyReply Direct Link To This Post Posted: 21 Jun 2019 at 9:17am
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20004 refi Mercury 60hp on Atomix. Gets 1.8nm/l. According to my simrad and what I calculate when I refuel. Done 1000hrs. Speed is what I can handle on the day. Usually 20kts at about 4000rpm suits me. 
No big issues so far. Would buy a similar motor but more modern any day. 

I can understand wanting more power for beach/surf launching. Perhaps get a lighter two stroke. Not sure which model would be good for you and fuel efficient.

Four blade prop to get on plane quickly sounds like a great idea. I know when I changed my mercury sport jet 175hp engine from 3 to 4 blade made a huge difference.


Here fishy, fishy fishy.... Nom, nom, nom
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Post Options Post Options   Likes (0) Likes(0)   Quote otdrmn Quote  Post ReplyReply Direct Link To This Post Posted: 21 Jun 2019 at 10:40am
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Steve, what pitch did you use for your 4 blade?
Sounds like some good numbers to be had by changing the fc535 to a 4 blade, I know it made a hell of a difference on my old Surtees.
I’m currently averaging 0.61L / Nm with a 60hp mercy command thrust (3 blade)

Cheers

G
The 4 R's ~ Rods, Reels, Rifles, Rooting
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Post Options Post Options   Likes (0) Likes(0)   Quote Joker Quote  Post ReplyReply Direct Link To This Post Posted: 24 Jun 2019 at 11:28am
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From memory it was a 13" pitch four blade.
I traded up 3 years ago.

Regarding the 60 CT you probably wont get much difference from a 4 blade as the command thrust is already spinning a high thrust propeller due to running the 75-115hp gearcase.
 
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Post Options Post Options   Likes (1) Likes(1)   Quote Rozboon Quote  Post ReplyReply Direct Link To This Post Posted: 24 Jun 2019 at 1:23pm
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The 70hp Yamaha is the same 1L block as the 50hp and 60hp, it just gets a 16 valve head and runs a different gearbox. Personally I'm not a huge fan of running the highest HP outboard from a given block.
All of the 60hp motors are running a 1L block, give or take a few CC.
We're running a 'zuk DF70A on a Stabi 1550 (similar size) and it has oodles of power, but it's almost the same weight as your 90hp Honda, which reflects that it's a much larger block.
The Honda 60 is the only one that runs a 3-cylinder motor, but it's a good one, very quiet and smooth despite the missing cylinder. A friend runs one on their 1550 and it also goes very well.

I don't have any experience with the Merc. They're all good motors these days, close enough that things like warranty and local dealer support can play a big part in which one you choose.


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Post Options Post Options   Likes (0) Likes(0)   Quote Big -Dave Quote  Post ReplyReply Direct Link To This Post Posted: 29 Jun 2019 at 9:25pm
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I see no real problem running the biggest horsepower in a certain block size, when was the last time you heard of a piston, Conrod crank failure, without a cooling or oiling issue involved.
you can't fix an idiot with duct tape, but it does muffle them for a while...
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Post Options Post Options   Likes (2) Likes(2)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 30 Jun 2019 at 10:08am
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For a good performance from your hull (chop, economy comfort etc), go max power rated for the boat...

 As to extras weight..it is not a 9' dingy.. its a near on a 5m boat.
The difference between motors is little more than a battery weight, less than most live bait tanks....
you may notice a slight difference at rest..in particular on the drift.. at anchor, the bow gets pulled down a little.
 And once under way stern lifts just as well if not better with good power and right prop.
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Post Options Post Options   Likes (0) Likes(0)   Quote lizid Quote  Post ReplyReply Direct Link To This Post Posted: 02 Jul 2019 at 2:42pm
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May have a very youthful Yammy F70 for sale. It's still running on my old tinny but have my Morgan now modded and repowered and have rapidly got used to the extra space. The F70, sitting on 4500rpm could leave Bowentown, go round the Mayor and back to the bar on 28 liters.
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Post Options Post Options   Likes (0) Likes(0)   Quote fishizzle Quote  Post ReplyReply Direct Link To This Post Posted: 18 Jul 2019 at 4:04pm
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I have a stabi 459 with a merc 2 stroke 50hp. About to upgrade to either  60HP or 70HP suzuki. This is what my mechanic said about the different brands. (They are in bayswater marina in AKL and service lots of working boats.)

Basically if your going to go from a 50HP to a 60HP, you may as well go all the way to 70hp (max for the boat spec is 75HP according to Stabicraft). The extra $1000 for quite a bit more performance when its more than just one in the boat. Engine size almost exactly the same, slightly heavier than my old 50H Merc.

Due to stabi buoyancy, he said id have no probs, so i rang stabi for a second opinion, and they said the same thing, go for the 70HP, max HP ratings are for just that, go max and your boat will rule.

My mechanic also said out of all the boats/motors etc they service, they said suzuki is better value for money, you pay more for Yamaha brand. Many they work on are well over 2000 hours and still going like new. So they recently put the bayswater marina runabouts (used every day) on 70HP Suzukis. 

Will post review/results when new engine is up and running next week.

Happy/safe boaitng everyone


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Post Options Post Options   Likes (0) Likes(0)   Quote Tirpits Quote  Post ReplyReply Direct Link To This Post Posted: 18 Jul 2019 at 11:30pm
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Hey fishizzle will be interesting to hear how you get on, I originally had a 70hp 2 stroke evinrude on mine and it performed fine-better at rest and towing then it is now. The 90hp Honda has more power but I spend most of my time drift fishing and water comes over the transom to much with the 90 on, there's a big weight difference between the two engines think theres quite a difference between the suzuki 60 and 70 hp as well? I always go for as much power as I can that's why I went to the 90(max rating for boat) but In my opinion I've stuffed what was a well balanced boat hence why I'm down sizing engine my other option is going to a 90 2 stroke but I do prefer 4 strokes
Cheers troy
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Post Options Post Options   Likes (0) Likes(0)   Quote fishizzle Quote  Post ReplyReply Direct Link To This Post Posted: 19 Jul 2019 at 10:16am
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SizeHey troy, thanks for your thoughts, super valauble, its funny, i decide today, and have noticed the weight diff too. the older 459 stabi which i have has the lower transom and was thinking it will get the slop over the back at rest way more than it already does. 

Weight of the 50HP 2stroke is basically 100kg, new 4 stroke 60HP suzi is 115kg, but jumps to 156KG for the 70hp. Not sure if its worth lugging around an extra 30kg on the bum for little gain. 

I just dug up the old spec sheet for the stabi 459 2002. it says max power is 60HP, but max engine weight of 175kg. When i rang stabi yesterady, they said a 70hp would be fine. 

My hunch tells me go with 60HP. Just because the older stabi is overall lighter, smaller and lowe at the back compared to a fully specd 1550. It has 200mm more length, full high transom...




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Post Options Post Options   Likes (0) Likes(0)   Quote Rozboon Quote  Post ReplyReply Direct Link To This Post Posted: 19 Jul 2019 at 11:26am
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The 70 Zuk is a huge motor compared to, for example, a Honda 60, or even the Zuk 60. It is quite literally 50% more motor than the 60, and the mid-range performance will reflect that, as it will have oodles more torque.
I think it will come down to how you need your boat to drive. If you want an epic hole-shot, or the ability to carry heaps of gear, or you're crossing bars and need that immediate leap, the 70 probably makes sense. If not, then a 60 is likely to still go really well, and is a smaller, less complex motor, which may save you some money in the long run as well.

I can see where you're coming from on the weight thing. Boats with low transoms put the ****s up me a bit. Water belongs outside the boat.
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Post Options Post Options   Likes (1) Likes(1)   Quote King Arthur Quote  Post ReplyReply Direct Link To This Post Posted: 19 Jul 2019 at 12:28pm
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Below is my opinion on motor weight on small boats say up to 5.5 metres. Hope is makes sense.

  From what I have experienced outboard weight can be a problem with engine pods and angled sides on small boats. Compare boats in regards to flotation at the back of the hull. Engine pods push the outboard weight off the back of the hull and angled sides reduce the beam at the water line leaving much less flotation in say the rear one metre of hull measured from where the outboard is mounted. Compare to no pod where the outboard weight is on the back of the hull and squarer sides increasing the beam at the water line. The second example, measuring from where the outboard is mounted, can have twice the flotation in the rear one metre of hull. How can this not make a difference in performance and stability on a small boat. On the first example at rest add two big guys fishing at the transom free board and stability can become a problem, not cool when water comes over a rear corner!

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Post Options Post Options   Likes (0) Likes(0)   Quote fishizzle Quote  Post ReplyReply Direct Link To This Post Posted: 19 Jul 2019 at 12:29pm
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I think your right Rozboon, im 95% an eastcoast fisher, often with lots of gear (kawau island overnight missions) but i do this with 50HP no probs. So i figure going up to a 60hp will be plenty. 
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Post Options Post Options   Likes (0) Likes(0)   Quote Rozboon Quote  Post ReplyReply Direct Link To This Post Posted: 19 Jul 2019 at 2:02pm
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Originally posted by King Arthur King Arthur wrote:

Below is my opinion on motor weight on small boats say up to 5.5 metres. Hope is makes sense.

  From what I have experienced outboard weight can be a problem with engine pods and angled sides on small boats. Compare boats in regards to flotation at the back of the hull. Engine pods push the outboard weight off the back of the hull and angled sides reduce the beam at the water line leaving much less flotation in say the rear one metre of hull measured from where the outboard is mounted. Compare to no pod where the outboard weight is on the back of the hull and squarer sides increasing the beam at the water line. The second example, measuring from where the outboard is mounted, can have twice the flotation in the rear one metre of hull. How can this not make a difference in performance and stability on a small boat. On the first example at rest add two big guys fishing at the transom free board and stability can become a problem, not cool when water comes over a rear corner!


This is where a huge difference in hull style arises, for example comparing a Stabi 1550 with Frewza F16 (both great little boats), the F16 has a pod and duckboard style stern, whereas the Stabi has the motor bolted to the rear plane of the full width of the hull. As you mentioned, lots more waterline beam at the point the motor is hanging off, so these boats will behave quite differently when weight is added to the stern.
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Post Options Post Options   Likes (0) Likes(0)   Quote Rozboon Quote  Post ReplyReply Direct Link To This Post Posted: 19 Jul 2019 at 2:06pm
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Originally posted by fishizzle fishizzle wrote:

I think your right Rozboon, im 95% an eastcoast fisher, often with lots of gear (kawau island overnight missions) but i do this with 50HP no probs. So i figure going up to a 60hp will be plenty. 

Just going to a 4 stroke will change the boat quite dramatically. The linearity of the power delivery makes them very easy to drive. 10hp extra won't hurt things, but the biggest bit you'll notice is the meat in the midrange.
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Post Options Post Options   Likes (0) Likes(0)   Quote Schampy Quote  Post ReplyReply Direct Link To This Post Posted: 19 Jul 2019 at 4:19pm
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A while back i had a 495 with a 70 hp 4 str yam. Went great but with tote tanks at the back and some scuba gear on board the engine was working pretty hard at times. 
The following boat had a full transom and a 70 suzuki 4 str. The extra 500 cc made a massive difference. It simply just lopped along no matter what was on board. where as the yam felt like it had to be reved hard to get similar speeds.
It pretty much just backs up what King Aurther wrote. The surtees with a platforms and a pod  suited the lighter engine... I tested one with a suzuki 70 on the back but it really pushed the bow up getting on the plane.
The 2nd boat with a full transom coped with the extra 35 kg suzi just fine and performed superbly thanks to the big block design.
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Post Options Post Options   Likes (1) Likes(1)   Quote Tirpits Quote  Post ReplyReply Direct Link To This Post Posted: 16 Aug 2019 at 6:32pm
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I ended up going yamaha 70 very happy with the service I got from power boat centre. Boat tows a hell of a lot nicer-it used to get the wobbles now I don't even no its there, boat doesn't have the holeshot the 90 did but when's she's on the plane and you hammer down she's not far of it. top speed is 61km versus 64 for the 90 and at rest it sits alot nicer in the water. Very happy can't wait to start using it.
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Post Options Post Options   Likes (0) Likes(0)   Quote Schampy Quote  Post ReplyReply Direct Link To This Post Posted: 16 Aug 2019 at 7:53pm
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Excellent stuff. The 70 yam has definitely proven itself as a reliable option over the last few years. Sure it does not have the punch of some of the other brands with large capacity blocks, but a 40 kg weight saving on the transom is a major draw card for alot of owners. 
Yamahas own 75 jumps up to 165kg. Total grunt fest with a 1.8 ltr block though.....
 
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