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Old 21 August 2014, 09:31   #1
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4.2m with 15hp ?

Guys what sort of speed would you get with a 15hp 2 stroke, on a 4.2m sib ?

Got the chance of a used 4.2 zodiac, not sure of the exact model as yet.
We have a 15hp engine here and want to keep it, for ease of handling etc.

Will it get the 4.2 up on a plane with a 150kg load of 2 people + kit ?
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Old 21 August 2014, 09:53   #2
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I would imagine over 20mph.
On our 3.8m sib we get 18mph with a 9.8hp and 24mph with a 20hp motor. Both two up plus gear.
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Old 21 August 2014, 10:46   #3
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That should be OK provided you manage to keep the weight down and not load on masses of extra kit.

You may find that it's a bit sluggish to get on the plane though which can be a pain where you've got enough chop to make you back off the throttle.
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Old 21 August 2014, 11:06   #4
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With that combo, and the weight you are mentioning, getting on plane should be doable. However it would be marginal, and a small amount of additional weight could make all the difference between getting on plane and not. If you can find and manage a more powerful motor, you will have a lot more leeway, and not need to add up every ounce of cargo (and inquire of your passenger's weight ) before setting out.

With a +4m boat, a trailer will make things much more safe and convenient, rather than assembling & disassembling with each use.

If you plan to assemble and disassemble each time, then having a van or pick up truck with a small hand crane, launching wheels (or launching dolly), and a good electric pump would make the assembly/disassembly far more pleasant and safe.
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Old 21 August 2014, 11:57   #5
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The boat would be kept on a trailer itself, but the motor needs to be stored elsewhere for security reasons so the 15 is a good weight for easy handling and lifting. The engine on the trolley rolls into the back of our estate car just fine.

Also, the boat needs to be able to be moved to and from the tailer - over a short stretch of sand and up and down a small slip ramp by hand - I have some large transom wheels here that I had planned to fit on the 3.8

I'm thinking with transom wheels the setup with a 15 engine would be more manageable to handle?

These wheels here -

NEW Large Boat Folding Launching Wheels Rib Inflatable + Bolts Stainless Steel | eBay
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Old 21 August 2014, 12:47   #6
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Quote:
Originally Posted by HighlandR View Post
I'm thinking with transom wheels the setup with a 15 engine would be more manageable to handle?
Definitely. In my experience a 15hp 2-stroke is the biggest that is easily manageable. Plenty of people do manhandle bigger engines, but it's hard work!
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Old 21 August 2014, 13:09   #7
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That's great John, we won't need much gear on board so keeping the weight to a minimum shouldn't be an issue, so help getting it to plane.

Will see if we can do a deal and possibly get this 4.2 - the extra space to move around would be a great plus too compared to a 3.8
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Old 21 August 2014, 13:17   #8
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It would be worth checking the weight of the 4.2 compared with the 3.8 before you make a final decision.
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Old 21 August 2014, 15:39   #9
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It sounds like you plan to deflate the boat every time? Depending on the floor type that could be a pretty heavy boat and the motor would lite in comparison. It also won't fold up/roll very small.

I would recommend a trailer for it. Run it with the 15hp, and if it is underpowered upgrade to a larger motor. On a trailer you won't have to deal with lifting the motor on and off.
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Old 21 August 2014, 16:06   #10
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Hi Peter, sorry I should have said on the last post, the boat will be kept inflated on the trailer... I recently got a motorbike trailer ( see photo ) and will be modifying that ( somehow ! ) and add bunks to rest the tubes on.

Any advice or pointers on converting this trailer would be a great help !

I just replaced the wheel bearings and will get new wheel rims very soon as the current rims are starting to look like the Titanic.

The thought of having to setup and pack away the boat every single time is really off-putting.

Also being permanently on the trailer is better option for the boat fabric and reduce wear and damage in the long term ?
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