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twin engine - slight mis-match advice/comments/your experience appreciated

T

tiverton.tom

New member
first, thanks for any replies!

I have had twin Honda 130s (3 years) and more recently twin 115s (4 years -1600 hours) on my big commercial RIB (rigid hull inflatable boat).

I am proposing to possibly go to 135s or 150s. One scenario is one of each, a slight mismatch of a 135 and a 150. They seem to be basically the same engine, other than the 150 is V-tech with the "boost" kicking in at 4500 rpms. .... ? We try to cruise at less than 4500 rpms anyway.

I am wondering if I would likely notice any/much difference.

Another option would be to replace one of my 115s with a second hand 130hp I have found ... or keep it "standby" in case of a problem with one.

My scenario is for all motors to be standard rotation with hydraulic steering.

thanks for your help!

tom
 
Good question... Most likely, if you keep the 135 and 150 at the same rpm you should be ok. You will always have to constantly be aware of the difference and it does not sound very safe to me. What happens if someone who is not familiar with the boat, pilots it? Just my opinion.

Your second option seems good to me...as long as your 115's are running good now. If you get the 130 and then have to use it as a back up...put the 115 throttle body on the 130 and you will have matched 115 motors again. It sounds like a cheaper solution too.

As I said...just my opinion..

Mike
 
No problem running different HP motors on the same boat.--------------Just match the RPM -----------------A rookie operator would soon see that they have to either adjust power or do a lot of steering work.
 
So, if both motors are standard rotation, and, the more powerful of the two was placed on the starboard side of the transom, would that have a tendency to help the boat track at full power? Or, would it be the other way around? I know, it's another question, I just couldn't help asking that's all.
 
This not a big deal at all----------------I put a 200 HP cover on one of my 235 HP motors ( twins ) just for the fun of hearing people explain to me how the two different motors was wrong , lots of fun listening to the " experts "
 
thanks for the replies.

I have heard back from someone on a different forum that they did not find any difference with a larger difference than my proposed 10-11%. I challenge anyone to please verify that they really believe that a 150 has 10% more power through the rpm range. ... at any rpm ? ... but YES I can understand at 4500 rpms the VTEC option on the 150 ONLY would give it more power. ... power is normally measured at the top rpms anyway ... isn't it?

... can someone help me find out data on testing these motors? ... I read somewhere that the YAMAHA 150hp tested at closer to 160 hp. I wonder if it is mostly marketing hype to have the biggest range of motors available to cover the most possible boats possible that have max. hp ratings. ... I heard that is why Yamaha changed the F100 to F90. ... a lot of boats had a maximum 90 hp rating ... and 75 - 90 - 115 makes more sense than 100 and 115 probably.

so ... you folks with twin motors - try this. .... just throttle back one motor 10% and see if you notice any difference. ... one at 4400 and one at 4000 rpms ... just to see. ........ well I was having a problem with one of the motors (was fuel filter blockage on one engine - they have separate filters) and I ran one about 10-15% less rpms so she didn't start sputtering til I figured it out.

"not safe" ... again I really appreciate the comments/dialogue ... but when does safety come into play, ... docking? ... so again, I ask ... am I really going to notice 10% more power on one engine (if there really truly IS 10% more power) when I'm coming slow into the dock.

http://marine.honda.com/Products/modeldetail/BF150

My main "safety" thing, is there going to be any hassles with insurance. The RIB is in fact used as a passenger carrying vessel, ... if it is commonly known (ha ha) that you shouldn't run mismatched engines, then maybe I could get into trouble ... even IF any problem had nothing to do with the mis-matched outboards. ... NOT SAFE!! (?)

WHY am I going through this exercise anyway? ... I have a brand new 135, ... they are (ALL) very expensive in Canada and I see that the 150 is far more popular with a lot of options to buy a slightly used one (in the USA). ... guy gave me a deposit yesterday on the twin 115s

thanks again for time!

tom in nova scotia
oceanexplorations dot ca (for Canada)
 
Take this into consideration.-------------When they hitch two horses onto a cart, how do you make the two horses each pull the same ??????
 
great point! ... they couldn't train animals to do the same thing with 10% or less difference. ... so I guess buggy tours with two horses are "safe" (?) ... what about 135 horses, ha ha
 
my insurance agent said "no problem" .... Honda can't guarantee me a delivery of a 135 til late spring ... taking a risk waiting for a 135 ... when there are a few second hand 150s (XL) out there (even if I have to buy and remove from a boat).
 
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