Mercury Pro XS 115 - Which Gear Casing?

Swordfish · 01 September 2022, 07:12

Hi All, can anyone help me out on this question please? Am I correct in thinking that for a small light hull the Mercury 115 Pro XS with the standard gear casing would be the correct choice as it will produce less drag. Whereas, for a larger, heavier boat the Command Thrust gear casing would be a better choice as it would allow for a lager diameter prop and could produce more torque for a better hole shot and enable lower speed plaining. Any advice greatly appreciated.

CJL · 01 September 2022, 20:14

Avoid the ProXs Versions. All they seem to do is shed silver paint!
They are very expensive compared to "regular" versions.

However the Command Thrust gearbox (which I think is available on regular and ProXs versions) will give you different gear ratios plus access to a wider range of props so you can fine tune the engine to suit your hull better.

Chris

Swordfish · 02 September 2022, 02:18

Thanks Chris, appreciate your advice. I'm still not sure that a small, light boat needs the larger diameter props that the CT gear casing allows for and will therefore just add drag unnecessarily. Totally agree with the CT / Prop variety benefits for larger hulls though. Will try to drop by Mercury stand at Southampton boat show and report back on the findings. Also a bit concerned about Olov's experience with this engine, if anyone else has experience with the Mercury 115 please do share: https://www.rib.net/forum/f8/zodiac-...-new-post.html

beerbelly · 02 September 2022, 05:30

i have the normal 115 ct on my humber destroyer 5.5 and i love it .using a 14.5x19p four blade mercury spitfire alloy prop its perfect cruises happily at 20 - 25 knots at around 4k rpm hits 6k rpm at 36 knots at around 8/10 throttle but the mid range punch in heavy sea is excellent .i have a 21p spitfire that gives me about 38 knots at wot at 6k rpm but i felt it softened that instant midrange pickup so prefer the 19p as i dont do much running flat out

Swordfish · 02 September 2022, 10:47

Thanks Beerbelly! Reassuring to hear some positive feedback on the 115 and that you are getting 6,000+ rpm. Seems like a good choice for a 5 to 5.5 m hull.

beerbelly · 02 September 2022, 13:59

Quote:

Originally Posted by Swordfish

Thanks Beerbelly! Reassuring to hear some positive feedback on the 115 and that you are getting 6,000+ rpm. Seems like a good choice for a 5 to 5.5 m hull.

to be perfectly honest i bought the comand thrust over the normal gearbox equipped outboard purely because i found a new one at a price i couldn't refuse but i have had no regrets it might be a knot or 2 down on top speed but that makes no difference to me

CJL · 04 September 2022, 17:18

The 115s are good engines and we've only had a few teething issues really.

Would buy again if we were looking.

Chris

Swordfish · 30 September 2022, 11:35

Thanks for all the advice! I just put the order in for a 115 Pro XS with the standard gear casing. Feedback from Mercury stand at Southampton boat show was that the CT was not necessary for the size/weight of boat I have.

With the standard casing I'm going for a 20" pitch prop, for the CT this would be 21" or 22" according to the Mercury calculator. Will report back on performance and how much silver paint comes off!

Note to self....buy rattle can of silver paint!