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Old 13 May 2016, 15:53   #1
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smaller prop to go slower at idle?

Hi,

I am doing a little swim relay across Lake Tahoe this summer with some friends and about 1000 other people I don't know :-) The way it works is it's a team of 6 swim across the lake while your boat putters next to you. in idle the 250 on the back of my 7m goes a whole lot faster than we can swim. I was wondering how much going to a smaller prop would help. It's a 6 hour cutoff time (we usually finish a good 5 minutes inside that) and I wasn't sure if I wanted to shift in and out of gear 1000 times that day. Is that a concern or do I just shift shift shift away? Will a different prop make much difference at idle? It would just be a a prop swap for the day. We'll be up there the week leading up and need the regular prop for daily fun. I did the race twice before in the old boat but it only had a carb'd 90 that made about 70 up there so no issues with too much speed.

thanks,
jason
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Old 13 May 2016, 16:04   #2
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Can you not borrow a 5 hp and stick it on the back? A large engine on long tick over is asking for trouble in my book.
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Old 13 May 2016, 16:12   #3
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Do you actually need to spend the whole time right alongside the swimmer or can you just be in the general area able to respond quickly if the need arises? Generally if you were say 10 feet from someone alongside you, given the turning circle of a typical RIB it would take more time to reposition to be able to pluck them out of the water than if you were a few dozen yards away and could turn onto course quickly to respond.
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Old 13 May 2016, 17:52   #4
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What size prop do you have, and whats the smallest you can easily find?
It will help. How much depends on that ratio.

Bear in mind if the prop is totally wrong and you brought a casualty on board you would lose top speed (and/or rev the life out the engine).

Clearly you need to swim faster. ;-)
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Old 13 May 2016, 20:21   #5
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Yes I do need to swim faster but that's not going to happen to any significant degree

Heres what I got.

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So the last time we did this swim there was a team with 4-5 guys from the Australian national open water team and a German of similar caliber. The came off the beach through the heard of boats way way way ahead of everyone with a big Australian flag flying shouting "God save the Queen!" They finished in just over 3 hours.

Yes you hang near the swimmer as the boat if your navigational reference. In years past navigation is the hardest parts. It's tough swimming a 10 mile straight line. This year I have the new GPS that will show me the straight line instead of from my current position.

Jason
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Old 13 May 2016, 22:49   #6
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Perhaps a trolling plate could work.
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Old 13 May 2016, 22:59   #7
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I'd just do the "let them get ahead and bump into gear" for a bit thing.

If your services are actually needed, you want the performance the correct prop will afford.

jky

I will add, though, that you'll likely need an inch or two less pitch to correct for altitude anyway. Should have said that up front.
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Old 13 May 2016, 23:30   #8
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A trolling plate looks like an idea but I'd hate to have to drill holes for one day.

I'm not too concerned about performance with too small a prop for one day. That's a far out chance and there are 150 other boats in shouting distance.

Smaller prop for altitude? Thinner air=less HP? How much better does a fuel injected engine handle the altitude? I know my old carbed Honda ran awful cause it was running rich with low land jets.

Jason
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Old 14 May 2016, 02:17   #9
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Now that I know what to look for there seem to be several options. They make trolling bags and some people just use a handy 5 gallon bucket.

Also trimming the engine up quite a bit will slow you down but people complain about lack of steering that way.

Ill have to try it out. I might sacrifice a bucket or two. They said a 1-2" hole in the bottom helps it orient better. They say the bags you can deploy from the front and not have to worry about buckets and lines off the back.

Jason
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Old 14 May 2016, 12:55   #10
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Buy an auction outboard or hire one if only for a day?

Even if you bought a used one and sold it you would lose a lot less money than buying a prop.... May even make money!
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