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Old 14-06-2016, 05:44   #1
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Join Date: Jun 2015
Location: Cruising the Keys
Boat: 1998 Manta 40
Posts: 40
Survey Results

Results of a survey on a 98 Manta 40 we currently have under contract.
Starboard and port engines were Volvo model# MD2030B. Recently the port sail drive was replaced with a Model 130SB and gear ratio 2:4. The starboard sail drive is probably original to the boat and was a Model 120SD with a gear ratio of 2:9. The sail drives were fitted with 2-blade folding props.

Has anyone else seen 2 sail drives on the same boat with differences in the gear reduction ratio? This may not amount to anything significant but I was curious any possible problems. I could not feel any difference at the helm but the rpms at the props would be different due to the different ratio's. The props diameter and pitch were the same.

Any thoughts or concerns?

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Old 14-06-2016, 06:04   #2
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Join Date: Dec 2006
Location: Brisbane Australia
Boat: Multihulls - cats and Tris
Posts: 4,862
Re: Survey Results

I wouldn't sweat it, you won't be using both engines a lot anyway, most cats go 80% of speed on one alone (approx) The only reason to use both is manoeuvring in marinas etc and in bar crossings and the like, I really dont think it will make much difference to you.
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Old 14-06-2016, 06:11   #3
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Join Date: Apr 2016
Location: Lake Belton, TX, USA, Earth: 3rd rock from the Sun
Boat: Vagabond 14
Posts: 421
Re: Survey Results

With different gear ratios they should have different pitch props, and that could balance the thrust pretty well.

As above, for most purposes, it would at worst mean not having both throttles at the same setting to make the boat track straight without having to hold significant rudder.
Full power on both could be quite a hand-full if they didn't compensate with the props.
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