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Old 11-11-2019, 14:45   #1
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Join Date: Apr 2019
Boat: Catalina 25
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Sizing battery wires for a Yamaha 9.9 hp

Hello!
Earlier this year I bought a Catalina 25 with a Yamaha Power Tilt 9.9.
I recently found that the wire from the battery to the outboard harness was a bad hack job, so I want to replace it with proper wiring.
As far as I can tell, the outboard harness is 6 feet, and I need to add another 7 to reach a point where I can connect the new wire to the harness through proper distribution posts.
The outboard is a Yamaha 9.9, I'm not sure how much the starter draws. The fuse on the outboard is rated 20 Amps.
If this is correct, and assuming 15 ft for the total wire (battery to harness + harness to outboard) an AWG 10 wire would do but... it feels weak.
Especially since the OEM Yamaha harness seems ticker, at least an 8, but I can't really tell, it's not standard wiring, it's encased in rubber and I don't want to cut it to see the wire size.
I was planning to go with AWG 8 or even 6, am I overengineering this?
While technically AWG 10 may do it, I feel like there wouldn't be much extra safety margin.
Has anybody extended the power wires for a small outboard? What would be the recommended wire gauge?
Thanks
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Old 11-11-2019, 16:10   #2
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Boat: Seawind 1000 XL
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Re: Sizing battery wires for a Yamaha 9.9 hp

I just bought 2 new yamaha 9.9s. They came with 8 foot power cables that appear to be 4 AWG. The fuse on the engine is just for the electronics, not the starter. If these are electric start models, you need 4 AWG or better. The power to my engines goes through a 64 Amp breaker so I think the starter current would be about 30 Amps.
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Old 11-11-2019, 17:49   #3
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Re: Sizing battery wires for a Yamaha 9.9 hp

[QUOTE=Richard Harper;3014020]I just bought 2 new yamaha 9.9s. They came with 8 foot power cables that appear to be 4 AWG.

I thought they were at least 4 AWG, but if you look at them, it looks like the insulation is thicker thank usual, which is why I think these may be smaller wires inside. I couldn't find any information on the gauge on the Yamaha site. or anywhere else on the Internet.

Quote:
Originally Posted by Richard Harper View Post
The fuse on the engine is just for the electronics, not the starter. If these are electric start models, you need 4 AWG or better. The power to my engines goes through a 64 Amp breaker so I think the starter current would be about 30 Amps.
I read the 15 HP version draws 32 amps, so I thougt mine would be under 30, but it doesn't hurt to be conservative. I guess I'll go with 4 (the cost of the wire is marginal) and take it from there.

Either way, it would be an improvement over what used to be there...
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