Join the C34 Association Today!
[C34 Home] [C34Tech Notes] [C34 Tech Wiki] [Join!]
Please login or register.
Advanced search  

News:

Pages: 1 [2]   Go Down

Author Topic: Cruising Speed/RPMs with Universal 25XP  (Read 443 times)

0 Members and 1 Guest are viewing this topic.

KWKloeber

  • Forum - Master Chief Petty Officer of the Navy
  • ********
  • Karma: 32
  • Posts: 3343
  • "Positive Impact" 1984 C-30 #3573 trbsfk M-25
    • View Profile
Re: Cruising Speed/RPMs with Universal 25XP
« Reply #15 on: August 04, 2019, 02:33:41 PM »

Less drag.


LOL  I meant he's measured speed over ground, how?   sorry.
Logged
Twenty years from now you'll be more disappointed by the things you didn't do, than by the ones you did.
So throw off the bowlines.  Sail away from the safe harbor.  Catch the tradewinds in your sails.
Explore.  Dream.  Discover.   -Mark Twain

Ted Pounds

  • Forum - Chief Petty Officer
  • ******
  • Karma: 8
  • Posts: 816
    • View Profile
Re: Cruising Speed/RPMs with Universal 25XP
« Reply #16 on: August 04, 2019, 05:16:56 PM »

Yes on both fronts.

speed how?

Ken has an important question.  If you're using GPS speed, but running against the tide your speed through the water may be in the proper range.  If you're using your knot/log how do you know it's accurate?  One way to use GPS to determine speed through the water and to check you speed in both directions and apply a little math...
Logged
Ted Pounds
"Molly Rose"
1987 #447

Ed Shankle

  • Forum - Petty Officer 1st Class
  • *****
  • Karma: 3
  • Posts: 338
    • View Profile
Re: Cruising Speed/RPMs with Universal 25XP
« Reply #17 on: August 04, 2019, 05:28:18 PM »

Hi SS,
If you are considering a new prop, I suggest checking out a folding prop. I got more motoring speed as well as sailing speed.
Also, as others are indicating, be sure to check you actual tach rpms with a laser device.

Regard,
Ed
Logged
Ed Shankle
Tail Wind #866 1989
Salem, MA

KWKloeber

  • Forum - Master Chief Petty Officer of the Navy
  • ********
  • Karma: 32
  • Posts: 3343
  • "Positive Impact" 1984 C-30 #3573 trbsfk M-25
    • View Profile
Re: Cruising Speed/RPMs with Universal 25XP
« Reply #18 on: August 04, 2019, 07:08:09 PM »


One way to use GPS to determine speed through the water and to check you speed in both directions and apply a little math...


Another is to use it to travel a known reasonably long distance, and apply a watch to calculatate average speed.  Bflo harbor breakwall has a marked measured mile, but if you use gps you're "off" the degraded amount only at the start and end so (just for a hypothetical example) say 30' over a mile or two or five.  If you use gps speed, it can be off the degraded amount (in this hypothetical again, 15' in any compass direction) on each and every reading it reports back.  If you are powerboating at 20 kts that's not significant, but......
Logged
Twenty years from now you'll be more disappointed by the things you didn't do, than by the ones you did.
So throw off the bowlines.  Sail away from the safe harbor.  Catch the tradewinds in your sails.
Explore.  Dream.  Discover.   -Mark Twain

Ron Hill

  • Forum - Master Chief Petty Officer of the Navy
  • ********
  • Karma: 52
  • Posts: 6709
    • View Profile
Re: Cruising Speed/RPMs with Universal 25XP
« Reply #19 on: August 05, 2019, 02:19:26 PM »

Guys : Look on the NAOA (sp?) charts in your location - there are numerous "measured miles" noted.

A thought
« Last Edit: August 09, 2019, 01:03:34 PM by Ron Hill »
Logged
Ron, Apache #788

sailr4

  • Forum - Petty Officer 2nd Class
  • ****
  • Karma: 2
  • Posts: 108
    • View Profile
Re: Cruising Speed/RPMs with Universal 25XP
« Reply #20 on: August 07, 2019, 11:03:42 AM »

A good rule of thumb is to determine your max RPM and cruise at 80%. So Floor It, then back off 20%.
Logged
Rob Fowler,1989 C34 #889 Tall/Wing, M25XP - No Worries, Coronado, CA

I'd rather be in a boat with a drink on the rocks, than in the drink with a boat on the rocks.

Ted Pounds

  • Forum - Chief Petty Officer
  • ******
  • Karma: 8
  • Posts: 816
    • View Profile
Re: Cruising Speed/RPMs with Universal 25XP
« Reply #21 on: August 08, 2019, 04:33:24 PM »


One way to use GPS to determine speed through the water and to check you speed in both directions and apply a little math...


Another is to use it to travel a known reasonably long distance, and apply a watch to calculatate average speed.  Bflo harbor breakwall has a marked measured mile, but if you use gps you're "off" the degraded amount only at the start and end so (just for a hypothetical example) say 30' over a mile or two or five.  If you use gps speed, it can be off the degraded amount (in this hypothetical again, 15' in any compass direction) on each and every reading it reports back.  If you are powerboating at 20 kts that's not significant, but......

Ken,
I think you’re missing my point. What he needs to determine is speed through water not speed over ground. The engine might be pushing the boat at 6 knots through the water, but if there’s a contrary current of 2 knots then GPS speed will only be 4 knots. And the same is true using a measured mile. 
Logged
Ted Pounds
"Molly Rose"
1987 #447

KWKloeber

  • Forum - Master Chief Petty Officer of the Navy
  • ********
  • Karma: 32
  • Posts: 3343
  • "Positive Impact" 1984 C-30 #3573 trbsfk M-25
    • View Profile
Re: Cruising Speed/RPMs with Universal 25XP
« Reply #22 on: August 08, 2019, 05:15:09 PM »

I ass/u/med he was checking max speed in flat/slack conditions because he seemed sure the speed determination was correct.  Surely he’d not be trying to measure if there was a current and not accounting for it.  Maybe a bad assumption?  :shock:

My comment was to eliminate gps error, not account for current.
Logged
Twenty years from now you'll be more disappointed by the things you didn't do, than by the ones you did.
So throw off the bowlines.  Sail away from the safe harbor.  Catch the tradewinds in your sails.
Explore.  Dream.  Discover.   -Mark Twain
Pages: 1 [2]   Go Up