Tohatsu 9.8hp o/b - underpowered for Jaguar 25?

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wfe1947

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When motoring around the harbour in relatively calm conditions, my Tohatsu 9.8 outboard will only push our Jaguar 25 at less than 4 knots. Any more and the engine sounds like it is being overworked.

Is this to be expected? Appreciate hearing your views.
 
:(:(

Someone else prob knows different, but, your engine with a 25ft boat, i'd say yes, thats about it, it would be regarded as an aux engine.

Having said that, suggest you check the prop, to see if its the best match for your auxillary power!

With small ob engines, the better prop is a 'Sail Drive', gives better low down thrust.
 
I would have thought a 9.8 hp was adequate for a 25 ft yacht.

Based on a wl length of 22 ft you expect a max speed of 6 and bit knots.
Maybe the prop you have is not well suited to a displacement hull. A finer pitch prop may well help esp if your engine is not reaching its max revs.

I believe Tohatsu offer "sail" versions of their outboards . As Cpt'n Popeye says this is what you should be looking at or at least the prop normally fitted to the sail versions.
Props are available for current models from 6.5" to 9.5".


However be sure your engine is running correctly.
If choking helps it suggests that it may need a carb clean
Also check that it is firing on both cylinders.
 
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Thanks for the comments, I will check he prop as the outboard (2009 model) came with th boat and my feeling is that the previous owner was more interested in appearance.

Carb should be OK as it has just been fully cleaned following it getting oiled up after I laid the engine down!!! Pretty sure both cylinders are firing correctly.
 
I had a 9.9hp on my Jag 25 and it was perfectly good. Get it serviced and check that it's got the right prop on it.
 
You really need a rev counter to be able to understand what is happening. I would expect on flat water with your boat to do at least 5knots so something is not right. Is the hull badly fouled? Is the prop slipping on its rubber bush? Is it just too big a prop? The starting point is whether the engine is reaching its design speed range 5-6000rpm or whatever.
 
You really need a rev counter to be able to understand what is happening.
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To which end a "Tiny Tach" might fit the bill.

There is a list of available props near the back of the owners manual
 
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:o
wfe1947 said:
When motoring around the harbour in relatively calm conditions, my Tohatsu 9.8 outboard will only push our Jaguar 25 at less than 4 knots. Any more and the engine sounds like it is being overworked.

Is this to be expected? Appreciate hearing your views.
Click to expand...

Is this with a 2stroke, and are you measuring your speed with a gps or log?

Tohatsu use Solas props, does your prop look like this one:

http://www.steeldevelopments.net/8-20-hp-propellers-approx-8-5-to-9-5-diameter-with-2-1-2-gearcase-1/4-blade-hi-thrust-aluminum-t8-series.html

This is the standard hi thrust prop.
 
A 10hp diesel drives my 26' heavy long keeler @ 6kts. It's going to be the prop. A friend had a 4hp longshaft on his Jaguar 22 and it was OK as long as the wind and sea conditions weren't too bad.
 
If that's the 9.8 two-stroke I believe they're quite sought after because of the power-to-weight ratio? It may be worth looking at selling and replacing with a 4 stroke or even offering a swap.
 
We have a 7.3 m trailable yacht weighs about 2 tonnes loaded with a 9.8 hp tohatsu we get 6.5 knots flat out but we use a 4 blade solas high thrust prop.

Used to have a 6hp and this would push us at 5.5 knots with same prop.
 
grumpy_o_g said:
If that's the 9.8 two-stroke I believe they're quite sought after because of the power-to-weight ratio? It may be worth looking at selling and replacing with a 4 stroke or even offering a swap.
Click to expand...

A 2009 model is not likely to be a 2stroke
 
northwind said:
Why? Apart from fuel economy, what mechanical benefit is there in the 4stroke?
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Much less noisy if that bothers you, otherwise the 2 strokers are very reliable and I would keep it if it has a long enough leg.
 
AngusMcDoon said:
No cavitation that I am aware of. Why do you think I have prop problems? Is 6.5 kts unreasonably slow for 10hp?
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I think, Angus, he was suggesting the Original Poster had prop problems, and to who he was directing the cavitation question.

10hp engines will mainly be sold for powering lightweight boats much faster. The standard prop gearing will be inappropriate for the weight of a 25ft yacht. The engine has enough power to move the boat at a good speed, but it won't be able to if the 'gearing' of the prop is wrong. It'll be like trying to pull away in top gear with a very heavily loaded car - the engine will be labouring and never reach enough revs for full power.

'Sail' versions of such outboards will have much lower 'geared' prop (and usually a few other minor mods), specifically so they will push along a heavier, slower boat at a good speed. Alternatively, a different pitch prop can be bought to solve the problem (if this is what it is).
 
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