Help - SIB question Outboards

MustRib · 24 February 2007, 19:38

Hi..currently running a 2006 15hp Mariner 2 stroke (weighs 33kg)on my Honwave 3.8.
I have the chance to go to a 20hp Yamaha 2 stroke, 2005 model (weighs 46kg) ...
Am I going to gain anything here? Extra weight against 5 extra hp.
The makers plate on the boat says only rated to 20hp... but the Yam 25hp weighs the same as the 20hp, and I also have th chance of one of those.
Is it dangerous to exceed the makers plate by 5hp?

codprawn · 24 February 2007, 19:47

Depends on how you use the boat - if you are lugging it around all the time the weight could be a problem.

I wouldn't bother with the 20 - you aren't really gaining much but the 25 is a different story. If the weight is the same as the 20 I would definitely go for it.

No doubt the doom and gloom merchants will start pointing out you will invalidate your insurance and you must be locked up as being an evil deranged speed freak but what the hell.

There is this amazing control you can use if the power proves to be too much - it's called the throttle - you will use less fuel as well because the engine isn't working so hard!!!

My little Quicksilver 3.1 copes fine with a 4 stroke Suzuki 15hp that weighs 46kgs!!!

Mugshot · 24 February 2007, 20:40

Quote:

Originally Posted by codprawn

Depends on how you use the boat - if you are lugging it around all the time the weight could be a problem.

It depends if its trailered too of course. My SIB, a 3.5 Corsair was rated up to a 20hp, I put a 25hp Mariner on it, only thing it did was put a grin on my face. I had no problems at all.
My only worry was the engine bouncing about on the transom whilst it was towed, but a few well placed ropes and a lump of wood soon put my mind at rest.
I'd say go for it, just don't stray too far from the shore when you first gun it, just in case.
You'll soon know

MustRib · 24 February 2007, 20:56

thanks guys .. the boat is kept on a trailer in my garage (just fits) and the engine on the transom all the time so no lugging it about.

I have insurance (need it for launching) and sods law will say that I will need it some day....so worried about invalidating that.

The Mariner is fine...its only 6 hours old, runs great and starts fine..I just find that I am running around on full throttle all the time. I think the boat could handle more. I dont feel anxious at all when running full chat on the Mariner.
(what fun is that ...hee hee).

The Yam 2 stroke 20 and 25 hp weigh the same as the Honda 4 stroke 20hp recommended by Honda for the boat.
I think the crux of the question is ...does anyone have experience of the Mariner 15 and Yam 20 ? and...further to that... If I stuck with the Mariner, is there anything to be gained by changing the prop ? or some other gag to worm some more speed out of it?

Ta!

Mugshot · 24 February 2007, 21:04

What speed are you getting now?

Mugshot · 24 February 2007, 21:09

According to the Honda Marine site you're rated to 55kg.

MustRib · 24 February 2007, 21:10

thats really hard to say..I have no way of measuring as no handheld gps.
the whole rig is under 6 hours old. Some one told me you get 1 knot per 1 hp on this kind of a rig, which would mean around 15 knots.
I took my level 2 cert in a Humber 5 m with a 50 hp and had 27 knots up.
Full chat in the Honwave feels like maybe just over half that speed.

Mugshot · 24 February 2007, 21:30

When I had the 25hp on my SIB I'd get 25mph with 2 up, I tried 4 different props on it and couldnt get it to go any faster, it only made a difference when I over propped it, and then it went slower

MustRib · 24 February 2007, 21:59

Maybe I ought to get the 25hp Yam and put the hood from the 20hp on top!

Mugshot · 24 February 2007, 22:04

Quote:

Originally Posted by MustRib

Maybe I ought to get the 25hp Yam and put the hood from the 20hp on top!

Thats the idea, no one will ever know!

Poly · 24 February 2007, 22:09

Quote:

Originally Posted by MustRib

Maybe I ought to get the 25hp Yam and put the hood from the 20hp on top!

Or can you get the cheaper 20HP and uprate it by replacing carbs?

I have the 20HP myself so would be interested to know.

I think you will notice the difference from 15-20HP though (I have no direct comparison as not tried 15 HP on my boat). Its possibly misleading to think of this as adding just 5 extra HP - but rather think of adding 33% extra power.

I don't know how HP varies with throttle on the yam but if it is linear (i.e. 3/4 throttle is 15 HP on the 20HP model) then you WILL notice the difference. On my boat 3/4 to full throttle is at least 5 knots difference in the flat.

MustRib · 24 February 2007, 23:04

thanks for that....
The Yam model is a new - but 2005 2 stroke engine....So any hints and tips that you peeps have on the motor would be appreciated.

ian parkes · 27 February 2007, 00:49

I had the same boat last year , with a 20 honda .

Get the 25 yam it won't be a problem for sure .
I went for the honda for economy , but the amount of fuel it used was so little I wished at times I had the extra power .

As for speed mine used to do 18 kts flat out with 3 people in , probably 20 plus with one but was very twitchy unless it was calm , so be careful till you get used to the motor and the way it handles .

MustRib · 27 February 2007, 04:28

thanks Ian...
I have decided to get the 20hp ...
Will post here when I get it fitted and have had a try (weather permitting!)