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Old 28 August 2019, 14:39   #1
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Best trolling prop size for fuel economy

Cheers from the other side of the pond. I have a zodiac hurricane 540 rib with a 90hp 2 stroke in which i am a safety boat for a "long" kayak race on a river.

It's 340 miles or approx 550 km. I will be doing a large majority (99%) of it just boating at the speed of a paddling kayak, approx 7 knots with river current. (There is a strong current on the river)

Fuel stops are spread out, so i'd like to maximize my range.

I am familiar with prop sizing for ideal RPM at WOT and cruising speeds on plane, however since i'll be going for such a long distance not on plane, rather just floating at little above 2k rpms, would going UP in prop diameter yield better fuel economy?

For example going from a 19p to a 21pitch, allows me to lower the rpms slightly to achieve same speed?

I know this seems trivial, but curiosity has me wondering. Thank you
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Old 29 August 2019, 01:02   #2
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I suspect the 2 stroke won’t enjoy that trip. Too slow for too long, they like to be rev’d to keep themselves clean.
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Old 29 August 2019, 05:54   #3
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if it drops you 300rpm would you see the difference.as said i would want to give her a blast now and then
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Old 29 August 2019, 06:21   #4
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Surely if you are following a kayak in a 7kn current, you will only be at tick over anyway. Going up a prop pitch might make you too fast & pass the kayak. Also the slower your RPM the less steerage you’ll have, especially in a following current. The comments about the engine oiling are also relevant, perversely you might need to go down a pitch to keep your revs up.
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Old 29 August 2019, 06:39   #5
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average speed of a kayak depending on design = 3 mph river doing just over 8 mph i think i would do catch up or use an auxiliary engine with a two smoke OMO
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Old 29 August 2019, 07:57   #6
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Thank you for the comments. I will have the opportunity to clear it out now and then as well. I will load up on spark plugs and if i start fouling them i will improvise something. I do have a small kicker (2hp) that may just be perfect for staying in the current.
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Old 29 August 2019, 08:52   #7
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I would use the 2hp and fit a long handle on the engine so you can sit on top of the 90hp and just steer, that is going to be a long trip. What will the weather be like? if its hot take a sunshade.

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Old 29 August 2019, 13:15   #8
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Quote:
Originally Posted by Pete7 View Post
I would use the 2hp and fit a long handle on the engine so you can sit on top of the 90hp and just steer, that is going to be a long trip. What will the weather be like? if its hot take a sunshade.



Pete





Particularly like the bimini!
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