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High altitude boat moving to sea level.

 
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Schuster



Joined: 25 Mar 2009
Posts: 117
City/Region: Port Orchard
State or Province: WA
C-Dory Year: 2007
C-Dory Model: 25 Cruiser
Vessel Name: Sea Witch
Photos: Sea Witch
PostPosted: Sat May 01, 2021 12:32 pm    Post subject: High altitude boat moving to sea level. Reply with quote

Does anyone out there know what I should expect when moving a boat that lives at high altitude (5,000ft) and move it for operation at sea level. Will it run stronger or weaker?
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garyf



Joined: 01 Sep 2015
Posts: 167
City/Region: Lincoln
State or Province: CA
C-Dory Year: 1991
C-Dory Model: 22 Cruiser
Vessel Name: C-Story
Photos: C-Story
PostPosted: Sat May 01, 2021 2:50 pm    Post subject: Reply with quote

I'll be interested to see the other replies, but I think it depends on the current prop. If the previous owner took time and effort to prop it for high altitude, there might be some room for improvement at lower altitude. If the current prop was intended for sea level, then it'll probably run a bit stronger.

Without any other influence like that, it should run a bit stronger in general.

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C-Story
'91 22 ft Cruiser
'08 Yamaha 90
KC3PO
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Hunkydory



Joined: 28 Mar 2005
Posts: 2652
City/Region: Cokeville, Wyoming
State or Province: WY
C-Dory Year: 2000
C-Dory Model: 22 Cruiser
Vessel Name: Hunkydory
Photos: Hunkydory-Jay-and-Jolee
PostPosted: Sat May 01, 2021 3:50 pm    Post subject: Reply with quote

Our primary boating is done at sea level & Yellowstone lake at 7733 feet. In between it’s all 6 to 7 thousand feet except for 3563 foot, present lake Powell. We’ve been going up & down these elevations for the now 19 seasons in our CD 22. You lose about 3 % of hp for every 1000 feet of elevation gained, so on Lake Yellowstone our combined 60 hp Honda’s of 120 hp are putting out only a max of 95 hp. To carry heavy loads on Yellowstone Lake, I use a 13 pitch three blade prop. Lake Powell to sea level 15 pitch. If ones prop is pitched on the high side, but workable at sea level, many will have to drop pitch for Lake Powell & definitely for Yellowstone Lake. The opposite for going high elevation to low. You will definitely have more power & probably will need to go to a higher pitch prop to keep from over rpming the motor by going from 5000 feet to sea level.

Jay

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Jay and Jolee 2000 22 CD cruiser Hunkydory
I will not waste my days in trying to prolong them------Jack London
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thataway



Joined: 02 Nov 2003
Posts: 20779
City/Region: Pensacola
State or Province: FL
C-Dory Year: 2007
C-Dory Model: 25 Cruiser
Vessel Name: thataway
Photos: Thataway
PostPosted: Sat May 01, 2021 9:42 pm    Post subject: Reply with quote

You will want to get max speed at WOT. What is the speed of the boat and the RPM at wide open throttle (engine and boat will help).

Generally increase pitch 2"--but it is possible that you may be able to increase pitch 3 or 4 inches...But we need to know the numbers.

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Bob Austin
Thataway
Thataway (Ex Seaweed) 2007 25 C Dory May 2018 to Oct. 2021
Thisaway 2006 22' CDory November 2011 to May 2018
Caracal 18 140 Suzuki 2007 to present
Thataway TomCat 255 150 Suzukis June 2006 thru August 2011
C Pelican; 1992, 22 Cruiser, 2002 thru 2006
Frequent Sea; 2003 C D 25, 2007 thru 2009
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Home port: Pensacola FL
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C-Green



Joined: 12 Apr 2004
Posts: 310
City/Region: Houghton
State or Province: MI
C-Dory Year: 2002
C-Dory Model: 22 Cruiser
Vessel Name: C-Green
Photos: C-Green
PostPosted: Sat May 01, 2021 10:59 pm    Post subject: Reply with quote

Not a worry for most but if your engine is carbureted, jets may need to be replaced.

Jay
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Schuster



Joined: 25 Mar 2009
Posts: 117
City/Region: Port Orchard
State or Province: WA
C-Dory Year: 2007
C-Dory Model: 25 Cruiser
Vessel Name: Sea Witch
Photos: Sea Witch
PostPosted: Sun May 02, 2021 11:16 am    Post subject: Reply with quote

Good info, thank you. I don't have numbers yet, but will be looking into this more when I do. Thanks everyone, you have been very helpful.
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