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Old 04 May 2007, 17:40   #1
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Ribcraft 5.3 Top Speed

Hi,

I was wondering what kind of top speed I should be looking at for a Ribcraft 5.3 with a Mariner 90HP 4 stroke on the back. I have touched just over 35 knots with one up and about half a tank of fuel at just over 6000rpm. Does this sound about right or should I be getting a bit more? Would anyone have any suggestions on optimum prop selection to run on this set up??

Cheers,

Neil
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Old 04 May 2007, 18:15   #2
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Not necessarily a fair comparison but my Ribtec 535 with a 90 mariner, 2 adults and 3/4 tank of fuel will touch 34 knts

Andrew
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Old 04 May 2007, 18:30   #3
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Well if wanted to squeeze a little more out of it you could try some different props. But I recon you're already on the money! You'll only gain a knott or three, is it worth the aggrivation and cost?
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Old 05 May 2007, 01:57   #4
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Well if wanted to squeeze a little more out of it you could try some different props. But I recon you're already on the money! You'll only gain a knott or three, is it worth the aggrivation and cost?
I think Andy's right-depending on use. If you usually use it solo then you could probably go up a couple of inches in pitch. 6k RPM is right on the top end of the recommended WOT rpm for a mariner 90 4st.
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Old 05 May 2007, 04:09   #5
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I think Andy's right-depending on use. If you usually use it solo then you could probably go up a couple of inches in pitch. 6k RPM is right on the top end of the recommended WOT rpm for a mariner 90 4st.
Quite agree with Matt - I think my manual recommends 5k - 5.5k RPM. If memory serves correct increasing pitch by 2" will drop WOT RPM by 250-400 RPM. This will increase top speed but reduce hole shot.

When I went from a 13.25" x 17" to 13.25 x 19" I got an extra 3-4 kts

HTH
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Old 05 May 2007, 17:34   #6
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Re:

Thanks guys,

Having used quite a few RIBS over the years as sailing support boats and coaching boats I realised that most of them never had GPS or any kind of speed indicators on them so I never thought about top speeds but having taken the plunge and paid for one myself with all the gadgets I was wondering was I squeezing every inch out of it that I could!! Delighted with the set up so far, just back from a cruise up the Liffey into the city and dinner over the far side of county Dublin, magic.

N
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