What size outboard

[Little yogi]

Hi

I'm thinking of buying a Shetland 4 plus 2, with an outboard engine.

The owner says I can the boat with or without the engine, which is currently a yamaha 2 stroke 80 hp, as I not really know the history of the engine or how many hours it has done, I'm thinking of buying the boat without the engine, then buy anew one mainly for piece of mind and reliability,.

Question is what size hp engine would be suitable for a 1.1 tonne grp boat for cruising the canals and rivers, looked on line and there seems to very ranging opinions.

Would anyone know how to do a calculation or know what's hp would be appropriate for such boat

Many thanks

 

[harvey38]

If it is only non-tidal work then 10 HP max, the only problem you may encounter at the low speed allowed on rivers is lack of steering but that could easily be overcome with an additional rudder bolted onto the shaft.

 

[penfold]

Depending on which river more than 10hp might be prudent, although 80hp is quite likely to be inappropriately powerful; I wouldn't fancy navigating the Thames or Humber with 10hp.

 

[mil1194]

Depending on which river more than 10hp might be prudent, although 80hp is quite likely to be inappropriately powerful; I wouldn't fancy navigating the Thames or Humber with 10hp.

Quite…. It could be the Severn…..

 

[harvey38]

Recommended is 25hp apparently but seen plenty Shetlands, Norman's etc pooling on the Thames with 10hp four strokes.

 

[mil1194]

Recommended is 25hp apparently but seen plenty Shetlands, Norman's etc pooling on the Thames with 10hp four strokes.

So are you thinking of cruising along the Thames?

 

[R400]

Is the Shetland a planing hull?

 

[ChromeDome]

It is stated to be semi displacement with the motor on a bracket, max hp is 90 but if you do not want it to be as fast as possible you can install a smaller,- 25 hp is suggested.

Mind you that ready-to-go weight will be higher than 1100 kg. Just add all the gear and equipment, stuff and crew you put on...

https://www.shetlandboats.co.uk/new-boats/shetland-245-3-2/

 

[R400]

Ah! Maybe not then

 

[ChromeDome]

I think it looks very well suited for inland use (the pics you find on the interweb confirms that this is what people do).

If budget allows I'd look for a 25 hp 4-stroke (presumably short leg) with a prop designed for work rather than speed, instruments etc.

 

[Little yogi]

Hi
Thanks for all your replies, I should have said the boat will be used on the river shannon in ireland, so non tidal and we are only using the boat for very relaxed cruising, at around 4 knots.

 

[ChromeDome]

Hi
Thanks for all your replies, I should have said the boat will be used on the river shannon in ireland, so non tidal and we are only using the boat for very relaxed cruising, at around 4 knots.

25 hp still would be right, IMO

 

[Little yogi]

Having never had a outboard engine before whats the difference between short leg and long leg ?

 

[QBhoy]

Thought I’d just mention that an 80hp Yamaha 2 stroke is one of the best engines ever made really. Wouldn’t be too quick to doubt it. Do a compression test on it for proof of decency if you like.

 

[Fire99]

Having never had a outboard engine before whats the difference between short leg and long leg ?

It's literally the length of the shaft / body between the powerhead (the engine bit at the top) and the prop. Outboards on for example dinghies usually are short shaft because the transom where the motor is mounted is close to the water and so just needs a short shaft. On a larger boat with a much deeper transom you may well want a long-shaft motor..

On engine size, I used to have a boat of similar size and it depends if you'll never want to go more than a bout 5 or 6kts or if you may get adventurous at some point and want to go faster or on fast flowing / tidal waters. I'd say on a 4+2 I'd go with a minimum of 25hp even if you stay on the inland waters. (If it's a 4stroke, it won't be upset tootling along) or something around an 80hp if you may change your cruising ground later. One issue you may have with a big outboard on the inland waterways, is unless you underprop it massively, the boat will probably want to do over 4kts the minute it engages gear and is above idle revs.

That's my random thoughts on the subject

 

[Boathook]

Yamaha do a 25hp high thrust outboard for displacement boats. May give around 7 or 8 knots top speed so possibly suitable for the OP.

 

[paradave]

It's literally the length of the shaft / body between the powerhead (the engine bit at the top) and the prop. Outboards on for example dinghies usually are short shaft because the transom where the motor is mounted is close to the water and so just needs a short shaft. On a larger boat with a much deeper transom you may well want a long-shaft motor..

On engine size, I used to have a boat of similar size and it depends if you'll never want to go more than a bout 5 or 6kts or if you may get adventurous at some point and want to go faster or on fast flowing / tidal waters. I'd say on a 4+2 I'd go with a minimum of 25hp even if you stay on the inland waters. (If it's a 4stroke, it won't be upset tootling along) or something around an 80hp if you may change your cruising ground later. One issue you may have with a big outboard on the inland waterways, is unless you underprop it massively, the boat will probably want to do over 4kts the minute it engages gear and is above idle revs.

That's my random thoughts on the subject

I’m not for a moment suggesting a large OB but my 130hp definitely doesn’t push me at 4Knts on engaging gear, more like 2. Quite a bit of leeway between stationary and 6knts.

If it’s tidal, I’d go larger than you think you need. I’ve been caught in a fast flood on the river, years ago, and was grateful for a large IB diesel as I think the river was running at about 7 knots.

 

[Rappey]

With 25hp you will be able to do 8/10 knts. More than enough. Pointless wasting fuel on a larger engine to only do 4knts.

 

[ChromeDome]

Having never had a outboard engine before whats the difference between short leg and long leg ?

Whereas leg = shaft in this context it needs to to match the height of the transom, from mounting point to keel of the hull:

And a 16 minutes info for you on two- versus four-stroke motors (direct comparison from 07:00)

In this case a Yamaha four-stroke, you may find other make(s) sounding a little different

About a year ago there was a thread about the Shetland 4 + 2

 

[Commercial Dave]

Everything about two stroke engines is horrible except for the weight. I don't understand why anyone who isn't regularly carrying the engine around would want one. Four stroke is better in every way other than power to weight ratio