Engine weight

[Wheeler a]

Want to purchase a four stroke for my sib . New 15 / 20 merc/ mariner comes in at 52 kgs my sib is rated at 50 kgs 15hp . Would it be ok to say fit a 15/20 hp to my sib at 52kgs . Thanks .

[jeffstevens763@g]

i would for 2kg have a look at the new yams they are supposed to be lighter

[Wheeler a]

Will do thanks

[jeffstevens763@g]

both 51 kg 15/20 standard shaft manual start very good engines

[Wheeler a]

So do you think even though my sib is rated 15hp / 50kg I could fit a 20 at 51 kgs .?

[jeffstevens763@g]

not knowing your boat and how its made or condition this is only my opinion others will spout insurance problems / harbour authorities etc. i would fit a 20 yes i would look at putting some strengtheners in from transom to floor if it's an ali floored boat you could get the decals changed to a 15 just being sensible with it would be my only concern.

[Wheeler a]

Thanks for advise . Got a air deck so can't strengthen at all . Maybe do some more research on engine weights .

[chipko]

Have you considered the Suzuki DF15/20 both come in at 44kg and have the benefit of EFI.

[jeffstevens763@g]

Originally Posted by chipko

Have you considered the Suzuki DF15/20 both come in at 44kg and have the benefit of EFI.

Ron Hale Marine Ltd - Suzuki DF15A

good call beat me to it

[Wheeler a]

Nice one have to look into it . Always been a merc / mariner person but sounds good ��

[chipko]

Originally Posted by Wheeler a

Nice one have to look into it . Always been a merc / mariner person but sounds good ��

Running a Mariner 60 now, seems good so far. Not sure much to choose between the big four/five brands. Had a Suzuki DF20A from new for three years and performed faultlessly...as would be expected.

[Wheeler a]

Sorry to bang on about weight issues but saw a honwave sib 2.7 m max hp 8 max kg 55 . Mine is 3.5 m max hp 15 max kg 50!.how does that work ?

[ShinyShoe]

Originally Posted by Wheeler a

Sorry to bang on about weight issues but saw a honwave sib 2.7 m max hp 8 max kg 55 . Mine is 3.5 m max hp 15 max kg 50!.how does that work ?

Because a designer was asked to specify a max and picked some numbers. They don't mean your boat disintegrates at that point, they mean a designer thought they would be OK for the boat's use, ran the numbers and decided they were safe so plated it up as such...

My guess would be 55kg means the glue is strong enough to handle that.

But if you put a 20hp on a 2.7m Sib with a shallow V it might become so skittish that the designer doesn't feel its safe to handle.

If a 15HP engine weighs less than 50kg and the designer of your 3.5 therefore stuck 50kg on as the weight. Why would he put 100kg on... you might think you can but a 70HP on!

Plus if you both have the same transom material but yours is longer (bigger boat = bigger beam?) then yours will bend more.

There has to be a dynamic in the weight and the engine force... probably with the boat load and the conditions too... a 55kg engine, 5HP over rating, shoving a maximum crew weight boat through a rough sea will be putting more strain on the transom than a 50kg, correct rated engine in the sea the boat was designed for.

I follow the logic of people picking up a second hand 55HP and putting it on a SR4 (rated to 50HP). The 55 probably doesn't out 55 anymore, and plenty of people have done it. It is using hull strength rather than glue on tubes. BUT I'm not sure I can see the logic of putting a brand new 20 on a boat rated to 15 and then "being careful". The whole reason you are wanting to over rate is because you want more punch at times...

2kg extra (4%) - I suspect not the issue. An extra 5 horses pulling at it I suspect might be! That is a 33% increase.

Did someone at one of the SIB gatherings not have some issues with their transom? Was it an over rated / over weight engine?

[Stevie Bill]

I think it was me that reported trimming/possible mounting issues at the recent Oban Sib meet. The funyak is rated to 25HP (early ones rated to 30!) But mine only fitted with 20hp so that not the issue... Although... My tohatsu is tiller steer and electric start and will be heavy for power output... so may need to check weight specs... Still working on the issue.

[ShinyShoe]

Stevie Bill - No not as recent as this year - maybe last year, maybe year before that? Wasn't there just think someone talked about a flappy transom!

Your Funyak should be fine with a 20 on it - so it must be trim/propsize.