15 to 25 on my SIB, worth it?

Jlomb436 · 26 July 2017, 18:55

Heya folks.

I had a post a couple of days ago regarding my 2 stroke (88' 2 stroke Mariner) shutting off on my a few times. It's likely my fault and my lack of experience.

However, it got me considering potentially upgrading to one of the new F25 Yamaha's. Outboards here seem to hold their value so much, I'd likely get a good return if I ever sold it or chose to upgrade.

My only question is performance. Currently, my boat cruises at 15 mph and tops out at 21. Topped out, it seems to chine walk a little bit and gets scary if there is anything but glassy ocean. The shaft is 17-18" inches. A new motor would allow for short which is what my boat requires.

I know this is variable, but do you think those fewer 2-3 inches would help with the squirrely top speeds? I'm also wondering if that extra 10 hp would get me another 3-5 mph top speed? Anyone have a good guess?

Thank you!

Boat 180 lbs
Fuel and gear 100 lbs
Engine (new) 126 lbs 82 lbs (old)
Me 200 lbs

jeffstevens763@g · 26 July 2017, 19:17

Hi mate

So you're running a long shaft on a short shaft transom which is 15 inches the long shaft will have an effect and possibly the bow twists from side to side putting more weight in the bow will lessen that effect but with a short shaft it will be spot on. My boat 3.65 m with a 25 Suzuki will do 22 knots similar weight to you running a 10 1/4 x 11 prop

Jlomb436 · 26 July 2017, 19:35

Quote:

Originally Posted by jeffstevens763@g

Hi mate

So you're running a long shaft on a short shaft transom which is 15 inches the long shaft will have an effect and possibly the bow twists from side to side putting more weight in the bow will lessen that effect but with a short shaft it will be spot on. My boat 3.65 m with a 25 Suzuki will do 22 knots similar weight to you running a 10 1/4 x 11 prop

Well, the motor is about 17.5" inches from the mounting brackets to cav plate. Would love the idea of not mixing oil either...

jeffstevens763@g · 26 July 2017, 19:51

Only my opinion but you will gain in few ways short shaft is right for you're boat 25 hp will give you more power than you will ever need a four stroke is smoother, quieter, better fuel consumption and no smell

Cheers