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Old 23 July 2010, 02:58   #11
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Country: UK - Scotland
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Boat name: stramash
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Originally Posted by alystra View Post
Phew! Will I ever get it right? 19" prop on today. Still does 6000 revs WOT (and the engine's only done 8 hours so it'll still be tight)

4000 revs with the old Merc 90 17" prop - 26.6 knots
4000 revs with new Honda 90 19" prop - 23 knots.

21" next ???
why ? your boats still going slower with a 19. You posted on this thread so I'm sure you read this post

http://rib.net/forum/showpost.php?p=360566&postcount=23

A 21 will kill that engine IMO, and thats before you load up the boat, how do I know this ?

My Bf90 was stock propped with an ally 13x19 which it ran fine with, I've said before though it had a lack of top end speed with that prop. So I changed it for a stainless one and gained about ....... a knot , but it slipped more from hole shot.
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Old 20 September 2014, 15:16   #12
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I feel the same on my Honda BF90D vtec which is installed on my 5.25m Rib I have a 13x19p and on Honda prop selector is indicating that I must have a 21p prop I noticed that the prop may be small as even with 4 persons on board I can plane in 3sec and it is consuming some full I think
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Old 22 September 2014, 18:33   #13
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Its a gutless engine ... if anything .. underprop it
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Old 23 September 2014, 05:18   #14
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Country: UK - Scotland
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Boat name: Moon Raker
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Old thread this. Now, with almost 300 hours on my engine I'm happy. The Honda 21" prop proved too high a pitch. I bought a SOLAS Rubex 3 19" prop. which seems to have more cupping than the 19" Honda prop I had originally.
Result, no ventilation unless I do silly things. Engine does rev more at any speed compared with the 21" prop, but it's more economical now.

Overall, I think there is little difference in performance of the boat with this Honda engine compared with the original Mercury 90 carbed 4str., but the engine revs. slightly faster at similar cruising speeds.

Biggest gripe is the Honda side mount control, which (compared to the old Mercury) is sloppy and imprecise from quarter throttle upwards. There is an inch of play at half throttle and beyond. This play is in the control, not the cable linkage to the engine, or in the engine. In rough water it makes engine control a bit hit and miss.

Compared to the Mercury, the Honda seems a much simpler design inside. Perhaps too simple. The dealer's mechanic seems to feel there's nothing wrong with it.
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Old 23 September 2014, 11:38   #15
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Quote:
Originally Posted by alystra View Post
Old thread this. Now, with almost 300 hours on my engine I'm happy. The Honda 21" prop proved too high a pitch. I bought a SOLAS Rubex 3 19" prop. which seems to have more cupping than the 19" Honda prop I had originally.
Result, no ventilation unless I do silly things. Engine does rev more at any speed compared with the 21" prop, but it's more economical now.

Overall, I think there is little difference in performance of the boat with this Honda engine compared with the original Mercury 90 carbed 4str., but the engine revs. slightly faster at similar cruising speeds.

Biggest gripe is the Honda side mount control, which (compared to the old Mercury) is sloppy and imprecise from quarter throttle upwards. There is an inch of play at half throttle and beyond. This play is in the control, not the cable linkage to the engine, or in the engine. In rough water it makes engine control a bit hit and miss.

Compared to the Mercury, the Honda seems a much simpler design inside. Perhaps too simple. The dealer's mechanic seems to feel there's nothing wrong with it.
what do you suggest to have a try with a 21pitc ? or gust stik with the 19pitch?my prop is black max by mercury
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Old 23 September 2014, 17:47   #16
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what do you suggest to have a try with a 21pitc ? or gust stik with the 19pitch?my prop is black max by mercury
Well, from my own experience, which is limited to one boat, I would keep with the 19" pitch. To my mind it's all about efficiency, and I originally started this thread by comparing my original Mercury 90 with my new Honda and noticing the difference in revs. for equivalent speed, thinking that fewer revs. meant better fuel economy. That thinking was wrong.

My Honda at 4200 revs uses less fuel per mile than the Mercury at 3800 revs, with boat speed about the same. It's all become a mystery to me and I've ceased to be too concerned. Now I just enjoy my RIBbing. :-)
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