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Old 11-04-2010, 11:32   #1
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Re-Powering a 42' Cat - Mercurys or Yahamas ?

Hello all. Here is the situation I am working on. I have a Crowther Spindrift 37 extended to 42.5 ft. It now has 2 older 9.9 High Thrust Yamaha outboards on it. They are getting a little tired and I would really like power trim and tilt. I am comparing two motors, and looking for opinions. Lord knows we all have opinions. These both can be had with 25" shafts which is a must.

Plan one: Replace with new Yamaha 9.9's that have trim and tilt with a 2.92 lower gear ratio and a three blade 11.75" prop turning 5000 to 6000 WOT. Displacement of 212 cc. This is my current setup.

Plan two: Replace with Mercury Pro Kicker 15's with 2.14 lower gear ratio and a 4 blade 10" prop turning 5000 to 6000 WOT. Displacement of 351 cc.

I am leaning towards the Merc's because of the higher horsepower but it is not clear to me that the smaller prop will help much with displacement speed I am running at. I know the Yamaha's are supposed to have good power in reverse, and they have worked pretty well for me but seem a little underpowered working into wind and wave.

Anybody have any thoughts.........Will I gain anything with the extra horsepower with the smaller props?
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Old 11-04-2010, 11:45   #2
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The merc props are smaller but the extra blade will more then make up for the reduced diameter
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Old 11-04-2010, 14:37   #3
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Another consideration: Specifications | BF20 | Marine | Honda MPE

Honda BF 20 "power thrust"

28 inch leg, power tilt, 62kg, 10x7 5/8" 4 blade prop.
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Old 11-04-2010, 15:05   #4
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Interesting. The last time I checked on Honda's nothing longer than a 20" was available. I will need to check them out and see how they fit my space. If they are close to the Merc's I will need to modify the motor wells on the boat. I did not find the 20 hp with the long shaft but did find the BF 15 with the 25 and 28 inch lowers. I really want to know if any of these 15's will improve my performance over the 9.9 Yamahas. Not much cavitation with the 25" shafts I have so will stay with them as the props are not below the keel of the boat which gives me a little protection for them in skinny water.
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Old 12-04-2010, 07:25   #5
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I think Honda "portables" (2-20HP) are available in a short (15" shaft), long (20" shaft), or extra long (25" shaft).

http://marine.honda.com/Products/models/portable

http://marine.honda.com/Products/models/midrange
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Old 12-04-2010, 08:08   #6
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Gord May continues to amaze us all.
I was just going to add that my 31ft was upgraded a couple of years ago from the standard Yanma 27hp to a Ruggerini 43hp. I motor just under hull speed on the river but against a wind and sea the extra HP is useful. Keeping a reasonable speed against wind ensures adequate steering and reduces the time exposed to discomfort. Apart from the initial cost there's little in running costs between larger and smaller engines. Too small flat out will need more maintenance, make more noise and add to stress.
I'm not clear whether you can steer these outboards as you fit them but obviously single engine running would be better if some steering can be applied, even if slowly. If you have cockpit controls then slow speed manoeuvring will be a easy anyway.
I would also add that separate fuel tanks will avoid both engines being affected together by low or dirty fuel.
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Old 12-04-2010, 08:36   #7
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My boat is set up that the motors are under the cockpit seats. They are not steerable. I have limited space to tilt the motors. I think any of the 9.9's will fit, but when I go to the 15 or 20's, which seem to be the same size with most mfg's, I will need to modify some. Not a real issue as I have been cutting and hacking on this boat since purchase 8 years ago. So far all seem to think more horsepower is a plus and disregard the prop size. Does anybody have any information on noise comparisons between mfg's?
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Old 12-04-2010, 08:55   #8
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There is another option. Put a generator inboard, under the hatches mentioned? Then add electric outboards. The bonus is that you get a light weight power unit that will also drive domestic electrical equipment and an outboard unit that is not readily sold on the open market. With the right kit your domestic batteries will allow for some manoeuvring to get you out of the marina on a quiet day and you can then crank up the genny or raise sails to suit. Have a search on t'internet to compare prices for each build.
The Outboard manufacturer's sites should give noise levels. I'd be a little worried if you can't tilt the props clear of the water. I get an extra knot or more by lifting the drive leg.
And there's always something to knock your prop on.
Have a good look on Ebay too, there are some good deals on Outboards from people like you, changing up or down for the new or old boat. And you're fitting two. They don't have to new to be reliable. You should get a good price for yours too.
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Old 12-04-2010, 11:46   #9
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No question on being able to tip up the props. Costs me about 3/4 knot to keep them down. I get a lot of noise from the drag too. I know much about electric o.b. but that makes a lot of sense. More decisions. Time for more research.

Thanks for all the thoughts folks...Keep them coming.
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Old 12-04-2010, 16:02   #10
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Quote:
Originally Posted by GordMay View Post
I think Honda "portables" (2-20HP) are available in a short (15" shaft), long (20" shaft), or extra long (25" shaft).

Honda Marine portable outboard engine models - 2 - 20 hp motors

Honda Marine Mid-range outboard engine models - 25 - 90 hp motors
The BF 20 is available in Australia with a 28 inch (703mm) leg and the "Power thrust" low pitch larger diameter prop: See "X Type"

Specifications | BF20 | Marine | Honda MPE

Maybe not available in the States though.
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Old 25-04-2010, 18:29   #11
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OK so here is the latest developments. Checked with my local Honda dealer, no 25" shafts on 20 HP motors and if I really wanted them they are back ordered until August.

Talked to another local dealer of Nissan, made by Tohotsu, same as Mercury, can get a 20 hp with extension kit and controls for about 1500 more than the 15 hp Mercs. These are all the same motors that Tohotsu builds. At least that is what I am told. The 15 and 20 hp motors are the exact same with different carbs and allowed to rev higher in the 20's.

So after reading and talking with a few more people and researching the prop situation, I have come to the conclusion that the Mercs with a custom prop from Solas for higher thrust in forward AND REVERSE looks like the way to go. This may take a while but I will try and remember to get back and give you all an update if I pull the trigger on these new motors.

Thanks, Cat Dan.
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