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Old 12 June 2014, 08:37   #1
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Country: Canada
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Boat name: white water
Make: zap cat
Length: 3m +
Engine: 50hp tohatsu
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tohastsu 50 hp needs to go faster

Hey iv got a 50hp mxd2 2013 .tohatsu. on a 14ft zapcat .
Iv got it going 45mph. But still far from what I want for speed
Iv got a D1 exausts
And a 10.2 x 15 ss prop
My reves 5100 wide open
Q: what els can I do for speed

Thanks joel babin
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Old 13 July 2014, 19:32   #2
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Slightly less pitch on the prop ,should realise the full rpm therefore the maximum power
Easy for me to say when I don't have to pay for the props
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Old 14 July 2014, 18:26   #3
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Boat name: Nautile
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Way low, that engine revs at 5850 when at wot, will need to go to at least 2 pitches down to raise rpm to near full wot numbers.

Happy Boating
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Old 16 July 2014, 04:00   #4
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I would keep the same prop, jack the engine up. you should easily hit the limiter with a 15p. Going down in pitch is not a fix for the problem.
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Old 16 July 2014, 14:55   #5
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If that was an aluminium prop I would agree "but it's not"
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Old 16 July 2014, 15:27   #6
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Quote:
Originally Posted by itrjoel View Post
Hey iv got a 50hp mxd2 2013 .tohatsu. on a 14ft zapcat .
Iv got it going 45mph. But still far from what I want for speed
Iv got a D1 exausts
And a 10.2 x 15 ss prop
My reves 5100 wide open
Q: what els can I do for speed

Thanks joel babin
You apparently at the largest engine size for the 14'0" zap cat.

How fast do you want (expect) to go for speed?

I cannot find a 50hp MXD2 Tohatsu spec :
Products/Tohatsu Outboard Motors

The M50 2-stroke Maximum operating range rpm 5150-5850

The MW50 2-stroke Maximum operating range rpm 5150-5850

The MX50 2-stroke maximum operating range rpm 5000-5800

The MD50 TLDI 2-stroke max operating range rpm 5150-585

The MFS50 4-stroke operating range 5000-6000

It seems that you are operating in or close to the bottom expected range of the engines.

You could try :
  • reducing the pitch.
  • reducing wind resistance.
  • reducing boat weight (less equipment)
  • try on smoother water i.e. no chop.
  • try on heading with the wind
  • reducing the number of persons on board
  • Using premium octane fuel rather than the supermarket brand.
  • Make sure that the cavitation plate is at the base of the transom +/- and not too much deeper i.e. too much drag.
  • Adding a pair of Deol fins

45mph in a 14'0" inflatable is a pretty good speed.

From this site

Tohatsu Outboard Motors - Propeller Chart

for a Stainless steel prop it sounds like you should have a 10.5 diameter 14" pitch and 3 blades Part# PT4050P14

How come you have a 10.2 diameter and not a 10.5 diameter prop?
Does it have 3 or 4 blades?
What else have you tried?
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Old 16 July 2014, 15:29   #7
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UNDER NO CIRCUMSTANCES SHOULD YOU EVER USE A PROP WHICH WILL ALLOW YOUR OUTBOARD TO OPERATE ABOVE THE OUTBOARD'S RECOMMENDED MAXIMUM RPMs!
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Old 16 July 2014, 15:49   #8
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I agree a 14p ss prop and possibly raise the engine so the cav plate is skimming the surface
This is a high performance set up and I know of similar lesser setups exceeding 50 mph
I don't think this is a family day out boat, it's a race boat (fun)
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Old 19 July 2014, 14:42   #9
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Have you had the prop worked? Get the blades sharpen and thinned! Will make a hell of a difference. Costs about 60
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Old 19 July 2014, 14:42   #10
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Don't go down in pitch...
I ran a standard tohatsu 50 with an 18p to the limiter (5850). This is on a thundercat (zapcat). You just have to lift the engine and get the trim right. If you cant get a 15p to the limiter on a light boat like ours there is a problem with the engine.

If you get the crank welded you can rev to 6500 safely.
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