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Suzuki Outboard Seajay Nomad Problem


Joeb

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I’ve got a Seajay Nomad HS 3.7 and had a Suzuki 15 2 stroke on it with 2 plus gear on board it would get up and go with a top speed of around 30kph 

i decided to add a floor to the boat and upgrade the transom to a LS and get a 20hp 4 stroke to compensate for the extra weight of the floor and some other bits and pieces all up about 50 kg extra including the motor 

Problem is now the best I can get out of it is 15kph flat chat 

the motor could come up about 25mm or so and it is running a 9 1/4 x 12 standard prop I have a 9 1/4 x 10 that I could try but not sure if I need to go down or up 

any advice much appreciated

cheers

joe

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Did you buy a new motor @Joeb and if so, were they part of the discussion regarding the upgrade? If so, I'd be contacting them to get their thoughts. I'm a bit rusty on speeds for tinnies - at 15km/h is it getting on the plane at all? Possibly a hydro foil could be worth considering? Or possibly look at shifting some weight around?

Good luck, let us know how you get on.

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What are the rpm's at WOT? 

The rev range at WOT will be in the owners manual. You want to be in the higher end of that range.  

If it's not hitting that upper range then you need to go down in pitch. The engine will have to much load on it not allowing it to rev out.

If it's over reving then you need to go up. The engine will be revving it's titts off before you hit WOT.  

Each prop pitch should change the RPM by about 300 to 500 rpm. So by going down to the 10 from the 12 that you have on, should see an increase in rpm between 600 to 1000 rpm. 

 

To give you an idea on the prop pitch, if you were to rotate the prop one rotation in a solid substance.....it's the distance the prop would move forward with one rotation.

So the 12 you have on will move 12inches forward in one rotation of the propeller. But because it's in water etc It won't in theory due to cavitation, weight of boat, water is easy to move etc. 

So the 10 would move 10inches in one rotation. You'll notice the 12 has deeper blades than the 10.

The engine will spin the 10 easier than the 12 due to it travelling less distance in one rotation. 

I hope that's easy to understand. I'm not very good at explaining techy stuff. 

 

You will need to get hold of a tachometer though. Call the dealer for help.

 

 

IMO the 20 will not go as well as the 15.

Sorry to say but four strokes don't rev and produce power like 2 strokes do.

My bro in law found that out. 

He had a 40 2 stroke and went to a 60 four stroke and tbh the boat went better with the 40. 

It's a 4.45m vnose punt. Stessle I think. 

I tried to convince him to get a 50 2 stroke but he went the four and was not impressed. 

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So I raised the motor up 25mm put my grandson and 40ltrs of water as ballast up front ( about 65kg total)  and off we went. Got up to 33kph and was reasonable at getting out of the hole. Thought all good job done

Today put my 100kg mate up the front and it struggled to get on the plane, so off with the 12”  put the 10” prop on and it would get onto the plane but it was slow 

Not sure where to go to from maybe a hydrofoil 

still have to take it to the weighbridge - so I’ll maybe do that tomorrow

Any suggestions most welcome

cheers

joe

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