Cruising Speed/RPMs with Universal 25XP

[KWKloeber]

Less drag.

LOL  I meant he's measured speed over ground, how?   sorry.

[Ted Pounds]

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...

[Ed Shankle]

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

[KWKloeber]

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......

[Ron Hill]

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

A thought

[sailr4]

A good rule of thumb is to determine your max RPM and cruise at 80%. So Floor It, then back off 20%.

[Ted Pounds]

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. 

[KWKloeber]

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? 

My comment was to eliminate gps error, not account for current.

[Bobg]

my 88 25xp gets 4.6 to 5 knots in calm water, empty boat no dinghy, at 2500 rpm, with a 15/10 3 blade prop.   used to get 6 knots can't figure out why I'm slower now but summer is so short here I quit looking for reasons why, seems like there is a huge disparity from one boat to the next even though the boats are the same,  Stu the thought of going close to 7 knots would make me a real happy sailor, a real wheee factor, grin

[Jim Hardesty]

my 88 25xp gets 4.6 to 5 knots in calm water, empty boat no dinghy, at 2500 rpm, with a 15/10 3 blade prop

Could it possibly be a slipping transmission?  I don't know how to test for that, other than look at the transmission fluid for discoloration.  Maybe a search here would give you a test to do, or someone may respond. 
Jim

[Sundance]

Maybe I can weigh in on this since now I can say I have owned an 89' with the 25xp and a 2001 with the M35BC. 

With the 25xp, 3 blade fixed prop (pitch unknown), 2500 rpm, fresh bottom, 5.2-5.5 kts.  By end of season I would only get about 4.8kts. Calm waters, no tide.

With the M35BC, 2 blade, 2500 rpm, VC-17 bottom paint, 6.5-7 kts.  Nearing end of season, nearly no difference. Calm waters, no tide.

I can say without a doubt the 25xp struggled as soon as there was any chop, wind, dirty bottom, etc.  The M35BC has the extra power that seems to push you through the chop and wind with ease and remain at cruising speed.

I've read for years about people with the 25xp motoring at 7+ kts.  Good for them, I have never even come close.

[Noah]

As they say "the devil is in the details". The last example is not a controlled experiment: different engines two different boats/hulls and, unknown calibration of instruments.

My 1990 sugar scoop stern boat, under power, with a 25XP, a 3-blade 15x10 Flex-o-Fold prop, a "calibrated" knot meter (checked against GPS and on measured mile), will do 7 knots in smooth water, at 2,800 RPM, (NOT calibrated tach) slack tide—with the sugar scoop stern buried. I have a hard bottom paint that is diver-cleaned monthly and a standard, lightly loaded boat. Just another anecdotal example.

[lazybone]

25xp,  Max-Prop 15 x 9.3  Calibrated 2500 rpm. 5.5 knots by gps.  Flat water, no wind.

  I'd give a testicle for 7 Knts.