Which outboard to buy?

[Denny]

Can anyone help please? I've recently bought a Cheverton Viking (ex ships lifeboat) which is a 16 ft displacement hull and want to buy an outboard engine (Yamaha). I intend to use the boat for fishing, which is a round trip of 15 miles from harbour. As the tides where I live are around 5 Knots would a 9.9 HP High Thrust or a 15/20 HP outboard be more efficient. I'm only really concerned about performance/reliability and engine efficiency not fuel economy.
Thanks for any advice,
Denny.

 

[jfm]

Can anyone help please? I've recently bought a Cheverton Viking (ex ships lifeboat) which is a 16 ft displacement hull and want to buy an outboard engine (Yamaha). I intend to use the boat for fishing, which is a round trip of 15 miles from harbour. As the tides where I live are around 5 Knots would a 9.9 HP High Thrust or a 15/20 HP outboard be more efficient. I'm only really concerned about performance/reliability and engine efficiency not fuel economy.
Thanks for any advice,
Denny.

I don't know the boat but googled it. Nice boat. It's heavy, and most seemed to be inboard engined. Just from looking at the pictures of them I'd have said 20hp but those I could find with hp stated seemed to have 20hp fitted so that confirms it - 20hp is the right power for the boat esp in tidal waters

BTW don't be duped by these "high thrust" engines. You can't beat the laws of physics. 9.9hp is 9.9hp and not a penny more

 

[tony345]

Don't buy Yamaha.

My experience with small Yamaha engines would make your blood boil.

I purchased a 5hp a few years ago - fine while under warranty - but then basically became more difficult to start until it wouldn't start at all.

Awful service from Yamaha dealers who say there is nothing wrong with it - but refuse to test it under load (ie it runs ok in our tank).

If i can get it to start at all - it usually fails within 10 mins and won't restart again.

I now have an outboard which cost several hundred pounds new, has been dealer serviced at the start of each season, but doesn't go - thanks Yamaha

 

[gjgm]

I don't know the boat but googled it. Nice boat. It's heavy, and most seemed to be inboard engined. Just from looking at the pictures of them I'd have said 20hp but those I could find with hp stated seemed to have 20hp fitted so that confirms it - 20hp is the right power for the boat esp in tidal waters

BTW don't be duped by these "high thrust" engines. You can't beat the laws of physics. 9.9hp is 9.9hp and not a penny more

Isnt it the gearing or prop that is different, though, as in higher torque, which is what you need here, not high revs.

 

[MVP]

We had an Oyster 16 fishing boat and re-powered it with a 15hp Johnson 4 stroke - went like a dream and sipped petrol

I don't think you will need any more power with a displacement hull, as you will just end up pushing water

PS, the 9.9s & 15 hp engines are basically the same, but the 9.9 is de-tuned to allow it to be used on U.S lakes (where 10hp is the limit)

Remember, 15hp today is probably at least 20hp on an older engine, where power was measured at the crank, rather than the prop

 

[Assassin]

How about another option, go for a small inboard of around 15-20Hp on a saildrive unit, it will not use any fuel to mean anything, and be much more durable than an outboard; if slightly more expensive initially.

Just a thought!!!! particularly as there are some good deals currently on new equipment, and plenty of good secondhand equipment currently on the market.

 

[Denny]

Thanks for all your replies, I've thought about fitting an inboard and might still do in the future, but one advantage with an outboard is that an engine change only takes minutes.

 

[jfm]

Isnt it the gearing or prop that is different, though, as in higher torque, which is what you need here, not high revs.

That's what their marketing folk would wish you to believe. Sure, on any outboard you can put a low pitch prop on to give you more thrust and less speed, just like changing your car from 4th gear to 2nd gear to get more torque at the wheels to get up a hill. But 9.9hp is still 9.9hp

 

[DorsetPete]

Consider a Diesel outboard - they last forever and are lots more reliable...
Cost a bit more tho!!!

 

[Kawasaki]

Can anyone help please? I've recently bought a Cheverton Viking (ex ships lifeboat) which is a 16 ft displacement hull and want to buy an outboard engine (Yamaha). I intend to use the boat for fishing, which is a round trip of 15 miles from harbour. As the tides where I live are around 5 Knots would a 9.9 HP High Thrust or a 15/20 HP outboard be more efficient. I'm only really concerned about performance/reliability and engine efficiency not fuel economy.
Thanks for any advice,
Denny.

In a way you have answered your own questions
You have a displacement hull 16ft boat
It will not do more than 8 kts.

That is the hull speed regardless of what power or type of engine you have
Outboard or Inboard.

Stick a 20hp on the back and all that will happen is the stern will dig in and you will waste fuel

There are no small diesel outboards.
Even if there were
Diesel technology has not 'been there' yet
A modern 4 stroke outboard is the way to go
Be it Yamaha , Honda or whatever
Do not be put off by a 'Yamaha' aint no good post
I,ve heard this kind of thing time and time again
I,ve been involved with Yamaha outboards, Motorcycles, Jet Skis
Same with Suzuki, Bikes Cars etc etc
Honda, bikes , cars even generators.
Kawasaki's (well that obvious) Bikes , jet skis etc

It's just sometimes a 'Retailer' will sell a unit and not be able to back up on the service side
Whatever the make
Sometimes peeps buy things off Flee Bay or whatever and 'damn' the manufacturer
Not saying this is the case with our Forumite friend who has had Yam troubles but this is what happens sometimes!

You need an engine that will 'push' the hull to it's designed max
If you are fishing in a place that has tides running to 5kts
You have to 'work' the tides.
IE , 'go with the flow' or else get a vessel that is 'semi displacement' that will do the bis through 5 kts no sweat.

A 16ft displacement boat does not need 20hp.

Yesterday, I was out in a 26ft Mitchell Sea Angler. (displacement boat)
35 hp Perkins in Her
We had 2 kts agin the tide, 14 with the tide.
It belts about, does the water in the Menai Strait!

Tother thing you have to consider
Depending on the transome height of your boat
Is whether you need a long shaft or short shaft outboard.

The pitch of the prop is important too as others have said
But this is just 'fine tuning'.

 

[AndieMac]

Tother thing you have to consider
Depending on the transome height of your boat
Is whether you need a long shaft or short shaft outboard.

The pitch of the prop is important too as others have said
But this is just 'fine tuning'.

That's right Kwacka, running a set-up in calm water with everything nice and horizontal with the cav. plate just below the surface, will change dramatically once the boat hits the undulating characteristics of wave action on a windy day.
The prop comes out of the water on each rise of the stern and boat speed drops significantly.

When I bought my new 15 hp long shaft aux., I tried the low pitch prop, lost 1knot of speed and no extra 'thrust', in fact seemed less, so put the original prop back on the shaft and the $250.00 back in my pocket.

 

[gjgm]

That's what their marketing folk would wish you to believe. Sure, on any outboard you can put a low pitch prop on to give you more thrust and less speed, just like changing your car from 4th gear to 2nd gear to get more torque at the wheels to get up a hill. But 9.9hp is still 9.9hp

It appears a great idea if you like going backwards !!
From Honda:

The combination of the 2.33:1 gear ratio and the 10" x 6 1/2" Power Thrust 4-blade propeller creates 60% more thrust in reverse and 15% more in forward. The result is improved maneuverability and performance

 

[tony345]

Just to clarify - I purchased a brand new current model engine, at full market price from a bona fide Yamaha dealer who had been (and still is) in business for years.

I did this because I wanted a reliable engine which would have full dealer backup and parts available if anything went wrong.

Unfortunately - that has not been my experience with Yamaha. I've owned all sorts of other outbards over the years and none of them have been as unreliable as this Yamaha.

I might as well have saved my cash and purchased something cheaper from flea bay - I'd have been no worse off.

Just recounting my own experience with this manufacturer and its appointed dealer.

 

[Hurricane]

I agree with jfm here - I think you need a little more power than the max required to push the boat at max displacement speed.
Reason - wind.
The effect of wind on any boat can be considerable so IMO, there is a good argument for a larger engine than the max required to push the boat's displacent speed.

So, it seems to me that 20HP would do the job.

Kawasaki - would you change your view in the light of this point?

 

[ontheplane]

JFM is right (ish) and also wrong.

Yes 9.9HP will always be 9.9HP - that's a fact.

However - Power gives you top speed and is a factor in acceleration - Torque and in this case THRUST is what pushes your boat through the water. Once it's on the plane, POWER will then push it up to it's top speed.... assuming it planes....

If it doesn't plane, to get it to a low %age of it's top speed, you need minimal power (they used to pull hundred tonne barges with one horsepower don't forget) at 2kts.

To add each additional knot, you need a large increase in power.

Once you reach hull speed it doesn't matter how much power you throw at it, it won't go any faster.

The only other factor would be windage - lots of that and you might need a bit more power to get it up to hull speed.

These high thrust engines are NOT marketing - they work well but only in the application they are designed for - i.e. pushing heavy boats slowly. You can certainly get away with a smaller engine to achieve the same speed with a high-thrust engine without a doubt, as it's gearbox and prop are set up to allow the engine to achieve maximum revs at displacement speed - thus using all that 9.9 hp.

I once had to borrow an engine as an auxilliary - I was doing a long passage in a 28' boat (approx 2.5 tonne, Planing hull) and didn't have a spare engine. I used a 40HP yamaha on a bracket, and before setting out, decided to try it to make sure it worked. It was rubbish!!! The engine was set up to drive a lightweight boat fast (inflatable or similar) it simply bogged down and wouldn't get above half revs - we got it up to 6kts on the GPS.

A guy on a nearby boat we'd known for years then lent us his 6hp saildrive evinrude (so that's 1/7th of the power) - we screwed it on the back and got 5.7kts on the GPS....! So logically - we could probably have used a 4hp and got about 5-5.5 kts...

I think a 9.9 would be fine for what you want - get either the hi-thrust engine, or at the very least fit it with the hi-thrust prop - you'll find it much better. I agree that 20hp is pointless, it won't go any better.

 

[Hurricane]

JFM is right (ish) and also wrong.

Yes 9.9HP will always be 9.9HP - that's a fact.

However - Power gives you top speed and is a factor in acceleration - Torque and in this case THRUST is what pushes your boat through the water. Once it's on the plane, POWER will then push it up to it's top speed.... assuming it planes....

If it doesn't plane, to get it to a low %age of it's top speed, you need minimal power (they used to pull hundred tonne barges with one horsepower don't forget) at 2kts.

To add each additional knot, you need a large increase in power.

Once you reach hull speed it doesn't matter how much power you throw at it, it won't go any faster.

The only other factor would be windage - lots of that and you might need a bit more power to get it up to hull speed.

These high thrust engines are NOT marketing - they work well but only in the application they are designed for - i.e. pushing heavy boats slowly. You can certainly get away with a smaller engine to achieve the same speed with a high-thrust engine without a doubt, as it's gearbox and prop are set up to allow the engine to achieve maximum revs at displacement speed - thus using all that 9.9 hp.

I once had to borrow an engine as an auxilliary - I was doing a long passage in a 28' boat (approx 2.5 tonne, Planing hull) and didn't have a spare engine. I used a 40HP yamaha on a bracket, and before setting out, decided to try it to make sure it worked. It was rubbish!!! The engine was set up to drive a lightweight boat fast (inflatable or similar) it simply bogged down and wouldn't get above half revs - we got it up to 6kts on the GPS.

A guy on a nearby boat we'd known for years then lent us his 6hp saildrive evinrude (so that's 1/7th of the power) - we screwed it on the back and got 5.7kts on the GPS....! So logically - we could probably have used a 4hp and got about 5-5.5 kts...

I think a 9.9 would be fine for what you want - get either the hi-thrust engine, or at the very least fit it with the hi-thrust prop - you'll find it much better. I agree that 20hp is pointless, it won't go any better.

I cant agree with your logic, I'm afraid.

I bet if you put the right prop on the 40 it would have gone equally as well - until max displacement speed of course - and maybe even have planed it. But crucially, there is extra power there if you need it.

jfm is only quoting the laws of physics - 9 hp is 9 hp - its the way you apply it that counts.

And as I say, I'd like to have a little power in reserve - to get out of any tricky spots you might get into.

I agree that it might not be any faster but sometimes you need extra power - wind is just an example - there are many other examples where extra power is really handy.

 

[mtb]

thats strange !

Don't buy Yamaha.

My experience with small Yamaha engines would make your blood boil.

I purchased a 5hp a few years ago - fine while under warranty - but then basically became more difficult to start until it wouldn't start at all.

Awful service from Yamaha dealers who say there is nothing wrong with it - but refuse to test it under load (ie it runs ok in our tank).

If i can get it to start at all - it usually fails within 10 mins and won't restart again.

I now have an outboard which cost several hundred pounds new, has been dealer serviced at the start of each season, but doesn't go - thanks Yamaha

I brought a 5hp over four years ago for £140, it's a reliable little thing. I had the usual sticking gear change which was due to the nylon part of the throttle arm which goes through the casing binding thus not allowing the gear change to move. I simply heated it enough to get it turning pulled it out file'd it until free. Aside from that No service in the time I've had it. I don't fix what isn't broke so perhaps you might have either a blocked jet or sticking needle valve. I was into marine engineering years ago and attended a Yamaha training day to get the service ticket. If you still have the old 5hp stuck in your shed I might give you a bad price for it

cheers
Mick