Outboard engine cc vs horsehpower help please!

[suffolktim]

Hey guys...so this has been confusing me for a while, and I just wanted to try and clear it up, so I can choose the right engine for my boat....

So I have an IP14 - it's the perfect fishing boat for our needs...it is easily launched by one person, without a car - comfortably fishes two people, and is nice and safe/stable. The only issue is the engine.

I curently have a Suzuki DT6 on her. Now with the tide we can get around 5 knots with the engine flat out, and against the tide - well...lets just say a wind against you and its a very slow journey home! The DT6 is an old 1993 2 stroke model, which doesnt apear to be a bad thing, as the older model is twin cylinder, only weighs 28kg and gives displacement of 170cc.

I am looking at increasing the engine size, without increasing the weight too drastically, to give us more speed through the water and extra power in reserve, and a lot of the 10HP engines ive been looking at, for example the tohatsu 9.8HP 2 stroke, have a higher HP, but little or no more displacement. The tohatsu I just mentioned seemed to be the perfect solution, but whilst it's 10HP and only 27kg, it is still only 170cc....the same as my 6hp engine!! If I fitted it, would I really notice the difference between the two engines?

I am quite confused by it all...and hope someone can help! I am led to believe the extra HP will allow higher revs, and potentially more speed, but will it really offer much more power?

Could anyone recommend a more suitable engine, if not the one mentioned above!

Cheers!!

 

[prv]

I don't know those particular engines, but it's quite common to have several in a range which use the same block and pistons but adjust the power by using different (or differently-tuned) carbs. So you might get say a 2.5hp, 4hp and 5hp which are really the same engine but at a different price.

Pete

 

[PCUK]

CC and horsepower have no connection. A saloon car with a 2000cc engine may produce 140hp. A racing car with a 2000cc engine may produce 400hp. It's the same size engine but the power is totally different. Your old 6hp 170cc is not as sophisticated as the newer 170cc engines which produce more power. Forget cc and concentrate on engine weight and power output. Yes, you will notice a huge difference between 6hp and 10hp.

 

[steve66]

Hey guys...so this has been confusing me for a while, and I just wanted to try and clear it up, so I can choose the right engine for my boat....

So I have an IP14 - it's the perfect fishing boat for our needs...it is easily launched by one person, without a car - comfortably fishes two people, and is nice and safe/stable. The only issue is the engine.

I curently have a Suzuki DT6 on her. Now with the tide we can get around 5 knots with the engine flat out, and against the tide - well...lets just say a wind against you and its a very slow journey home! The DT6 is an old 1993 2 stroke model, which doesnt apear to be a bad thing, as the older model is twin cylinder, only weighs 28kg and gives displacement of 170cc.

I am looking at increasing the engine size, without increasing the weight too drastically, to give us more speed through the water and extra power in reserve, and a lot of the 10HP engines ive been looking at, for example the tohatsu 9.8HP 2 stroke, have a higher HP, but little or no more displacement. The tohatsu I just mentioned seemed to be the perfect solution, but whilst it's 10HP and only 27kg, it is still only 170cc....the same as my 6hp engine!! If I fitted it, would I really notice the difference between the two engines?

I am quite confused by it all...and hope someone can help! I am led to believe the extra HP will allow higher revs, and potentially more speed, but will it really offer much more power?

Could anyone recommend a more suitable engine, if not the one mentioned above!

Cheers!![/QUOTE
Not quite that simple. A lot depends on the hull design. A displacement hull wont make much difference in speed with a larger engine, but there are plenty of folk on this forum with much more knowledge than myself

 

[Topcat47]

5 knots is about all you'll do with a comparable engine. You'll need a lot more power to get her up on the plane and that's the only way to get more speed. There's one for sale with a 60hp outboard, probably a bit overkill IMO, a 40 ought to be enough to plane a 14' cathedral hull, but in rough weather you'll not be able to use all that speed anyway. Choice of Propellor will also be critical, a friend with a sheltie (~18' ) found 55hp a little too much, but kept a 9hp trolling engine for when he was stuck in conditions that only allowed hull speed. He re-propped the 55 as the pitch on the original was a bit too fine.

You'd be better to post on the MoBo forum, as you'll get better advice.

 

[suffolktim]

Thanks for the input guys...the boat is a semi displacement hull, and speaking to a few owners of the same boat they say that they achieve around 12 knots with a 15hp tohatsu, but I would prefer the 10hp tohatsu due to weight, and was just confused to see it having the same cc as my old 6hp engine. Its good to know that the 10hp should have much more power...its just a shame theres never any way to actually test out how it performs without laying down cash and buying an engine first! Ah well! Again, thanks for all the replies!