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Old 28 August 2014, 20:16   #71
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Country: USA
Town: It's a Dry Heat, Arizona
Boat name: Foxtrot Charlie
Make: Zodiac FC470
Length: 4m +
Engine: Yamaha 90
Join Date: Aug 2014
Posts: 20
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Originally Posted by SIBRider View Post
Yamaha 90 is one big motor for F470.
Well it is and it isn't. HP yes, on paper, no question. Weight, not so much. It went down like this... I've run up through 55hp motors on these boats and was left wanting a little more power. With the hard deck the F470 is rated for 65hp, which isn't very common so I began looking for good deal on a Yamaha 70 hp 2stroke. After searching the better part of a year I came across a great deal on the 90, which is pretty much the same as the 70 (size, weight, etc) just more HP. In fact the Yamaha 70/90 weight is about the same as the Johnson 55hp Enforcer and my previous favorite Honda BF50...around 230#...so the 90hp motor isn't making it any more stern-heavy than the other commonly-used motors. So I figured I'd "try" it. If it turned out to be too much, I'd sell it and go back to plan A. Plus I could always install a throttle stop, right? (BTW, psychologists call this process "rationalizing" lol)

The newer F470s like mine have a straight transom with SUBSTANTIALLY beefed up mounting to the tubes (Zodiac calls them "Ovoid transom reinforcement patches"), furthermore I have all the components of the CMK installed: the stainless transom cap, the one piece solid stringers and the thrustboard reinforcement plates. I also added fittings to attach torque rods between the transom and aluminum hard deck to prevent excessive stress on the transom attachment. Finally, I run SeaStar full hydraulic steering. Long story short, the 90 is working fine on this particular F470. I've been running this setup for about 4 yrs now and other than the aforementioned transom backwash issue, I haven't observed any issues: No excessive fatigue on the transom or boat hull and no "scary" behavior—even at WOT in rough water.

Despite those assurances, I'm sure there will be those that disapprove of my setup. For those people, take solace in the fact I do plan to repower in the future. Yamaha finally came out with a lightweight (~250#) 70hp 4-stroke last year that I would like to eventually throw on the back on this boat. Then I can hang the 90 off the back of a 5.4m RIB

All this is probably better located in my build thread...as soon as I get around to starting it I'll move it there.
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Old 28 August 2014, 20:50   #72
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Country: USA
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Make: Zodiac F470
Length: 4m +
Engine: Suzuki DF25EL
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Posts: 229
Sounds good to me.
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Old 28 August 2014, 21:50   #73
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Country: USA
Town: It's a Dry Heat, Arizona
Boat name: Foxtrot Charlie
Make: Zodiac FC470
Length: 4m +
Engine: Yamaha 90
Join Date: Aug 2014
Posts: 20
Quote:
Originally Posted by SIBRider View Post
Sounds good to me.


Sorry for that somewhat lengthy response. I'm new here and not quite sure to expect yet... Truth be told I lost interest in the boats for a while and building this rig has rekindled my interest. I set out to build a flexible platform that I could SCUBA dive off one day and chase my PWC-owning friends around the lake the next and pretty much succeeded...this boat is a blast to drive.

I do have another FC470 I plan on keeping simple...just a roll up deck, co2 inflation, 6 gal fuel bladder and a small tiller outboard (25-35hp). Actually I'd love to get a FC420 but they seem to be as rare as hens teeth (anyone want to trade? ;-) )
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Old 30 August 2014, 16:02   #74
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Country: USA
Town: Cali
Boat name: Thumper
Make: Avon CRRC 4.5
Length: 4m +
Engine: Merc 50
Join Date: Jun 2012
Posts: 363
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Originally Posted by Attack Ducks View Post


Sorry for that somewhat lengthy response. I'm new here and not quite sure to expect yet... Truth be told I lost interest in the boats for a while and building this rig has rekindled my interest. I set out to build a flexible platform that I could SCUBA dive off one day and chase my PWC-owning friends around the lake the next and pretty much succeeded...this boat is a blast to drive.

I do have another FC470 I plan on keeping simple...just a roll up deck, co2 inflation, 6 gal fuel bladder and a small tiller outboard (25-35hp). Actually I'd love to get a FC420 but they seem to be as rare as hens teeth (anyone want to trade? ;-) )
You can't run a bigin....''You'll shoot your eye out''.

Carry on..
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Old 31 August 2014, 23:36   #75
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Country: USA
Town: It's a Dry Heat, Arizona
Boat name: Foxtrot Charlie
Make: Zodiac FC470
Length: 4m +
Engine: Yamaha 90
Join Date: Aug 2014
Posts: 20
An update on my experience... I went out this morning and raised my motor again. Unfortunately, the original holes through the transom were drilled 2nd down from top because at the time I never expected I would need to raise the motor (never had to before) . Previously I raised it one hole. So today its now two holes above flat on the transom. Unfortunately that's not enough I never really looked at it with the motor tilted down on the trailer until today...it's clearly too high, not sure how I never noticed this before. Looks like it needs to come up another 2" to be even with bottom of transom. To do it right I need to take the transom cap off and raise that also, inserting a suitable filler in the deadspace above the transom...which means removing the motor...fun!

The upside is the boat ran noticeably better today...much less splash over the transom than last weekend. I had an extra person in the boat today plus 16 gal of gas and some gear that I didn't carry last weekend. Despite that and the fact that the lake was choppy as heck (holiday weekend) I gained 3-4 mph top speed compared to last weekend. Some of that I attribute to running some seafoam through the motor yesterday to clean out the carb jets & carbon buildup...but I'd say 1-2 mph was just from raising the motor. Really curious to see how it does whien I find the "sweet spot" which I will be doing soon since I have to derig it anyway to fix a speed tube sheath (more on that in another thread). If it's not one thing, it's another!
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Old 01 September 2014, 03:29   #76
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Country: USA
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If it's not one thing, it's another!
Well, yeah; it's a boat. The only time you don't have something to work on is when you've sold it.

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Old 03 September 2014, 00:54   #77
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Country: Canada
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Make: Gemini
Length: 4m +
Engine: 40hp 2 str
Join Date: Oct 2003
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Despite those assurances, I'm sure there will be those that disapprove of my setup. For those people, take solace in the fact I do plan to repower in the future. Yamaha finally came out with a lightweight (~250#) 70hp 4-stroke last year that I would like to eventually throw on the back on this boat. Then I can hang the 90 off the back of a 5.4m RIB

All this is probably better located in my build thread...as soon as I get around to starting it I'll move it there.
If you do go to the Yam 70hp 4-stroke - I'd like to hear your thoughts on it. It will still be a while before I upgrade from my Yam 40hp 2-stroke, but that new Yam 70hp 4-str is on my short list, as well as a 65hp ETEC commercial and a Honda DF60. Am wanting to stay within the max that is rated on the transom plate which is 60kw (~80hp). Would want to stay with a tiller set up for me.
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