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Old 21 October 2007, 16:44   #1
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Twin outboard speed trials.

Out in the solent today, my brother and i experimented with the maximum speed reached on each engine running solo . Engines are 40hp Mariners top speed with for each engine was about 25mph, which means they seem to be set up equally, however maximum speed reached with both engines was only another 10mph, obviously acceleration and pulling power is greatly improved, and we like the directionally stability when using both engines, But does the top speed sound about right, would the boat go quicker with smaller props, or larger props ?
also when run together the engines i'm sure rev higher( no rev counter to confirm). Would appreciate any thought's on this.
Regards Paul.
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Old 21 October 2007, 17:08   #2
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Would you go quicker with 1 x 80hp? Half the weight and drag.
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Old 21 October 2007, 17:11   #3
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Out in the solent today, my brother and i experimented with the maximum speed reached on each engine running solo . Engines are 40hp Mariners top speed with for each engine was about 25mph, which means they seem to be set up equally, however maximum speed reached with both engines was only another 10mph, obviously acceleration and pulling power is greatly improved, and we like the directionally stability when using both engines, But does the top speed sound about right, would the boat go quicker with smaller props, or larger props ?
also when run together the engines i'm sure rev higher( no rev counter to confirm). Would appreciate any thought's on this.
Regards Paul.
It's all about gearing. Strap two minis together and run 'em down a track, they're not gonna do 150mph. The ONLY advantage of running a pair is safety.
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Old 21 October 2007, 17:16   #4
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top speed with for each engine was about 25mph
That sounds high for one engine on that set up. Did you go from a standing start on one engine or get up to planing speed and then throttle back one engine.

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when run together the engines i'm sure rev higher
They will do. Running on just one engine you're overpropped.


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Would you go quicker with 1 x 80hp?
Yes. About 3/4 knots
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Old 21 October 2007, 17:21   #5
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Makes sense about the gearing, not in the position to change the engines just yet, so far they have been reliable if not a bit juicy to run, from the safety aspect more often than not, out with young children, so that is good to have, what speed would i expect with one 80 hp as suggested though.
Paul.
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Old 21 October 2007, 17:24   #6
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The ONLY advantage of running a pair is safety.

Not forgetting better roll stability and increased slow speed manouvrebility
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Old 21 October 2007, 17:25   #7
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one engine up, and throttled from standstill, with 2 adults and 2 small children.
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Old 21 October 2007, 17:27   #8
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The ONLY advantage of running a pair is safety.
Two engines look more sexual.
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Old 21 October 2007, 17:30   #9
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Makes sense about the gearing, not in the position to change the engines just yet, so far they have been reliable if not a bit juicy to run, from the safety aspect more often than not, out with young children, so that is good to have, what speed would i expect with one 80 hp as suggested though.
Paul.
If you're gonna go to the bother of re-engining you might aswell go to max design hp. It'll say on the plate what that is. 5.3-5.5m ribs are usually around 90hp.
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Old 21 October 2007, 17:31   #10
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The ONLY advantage of running a pair is safety.
Yes, you're quite right there. If one engine breaks down, you'll have an available source of spare parts on the other one
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