Real World Performance Numbers

General boating discussion
BroadCove
Posts: 47
Joined: Mon Jan 14, 2008 12:40 pm
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Location: Casco Bay, Maine

Real World Performance Numbers

#1

Post by BroadCove »

I've got a Pacific that lives for five months of the year on a mooring in southern Maine and for the rest of the time on a trailer in the yard. The bottom is not painted, but I'm usually pretty good at giving the hull a decent scrub every month or so while we're hanging out on an island beach. Not so this year - I haven't touched the bottom since the boat went in near the end of May. I just pulled it out of the water on Saturday in advance of Irene and am 2/3 of the way through power washing the bottom. I thought some of you might be interested in a "before and after" performance post. I'm personally curious how much difference a clean/dirty bottom makes - I know it's "alot" but not exactly how much.

I should have recorded numbers throughout the rpm range, but I didn't think to do this until near the end of the day and so just got numbers at WOT. I'll post the follow-up after I get the boat back in the water later this week.

Boat: 26' Pacific HT, Suzuki 250 w/ 3 blade 15.25 x 19 prop
Load: 50 gals. fuel, 4 adults, 7 kids (9 - 15 yrs.), 3 dogs (small, medium and large) and assorted crap - my "real world" numbers!
Bottom: Dirty as sin (should have taken a picture, but trust me, it was "hairy")
Conditions: Air temp 75F, water temp 65F, light chop
WOT: 32 knots @ 5500 rpm, 21 gals. per hour (about 1.5 kts/gal)

With a relatively light load (for me) and clean bottom, the boat will hit the Suzuki's 6100 rpm redline. I'm thinking that the dirty bottom robs me of 5-6 knots and 0.2-3 kts/gal at WOT. We'll see what the final results are, and I'll try to post numbers from the full rpm range.
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goatram
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Re: Real World Performance Numbers

#2

Post by goatram »

A couple of pics would have helped to visualize it.
I left mine in the water for 5 days and I got a scum line on the boat and motor.
John Risser aka goatram
33' RBW with twin 250 Hondas (Aliens)
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cape steve
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Re: Real World Performance Numbers

#3

Post by cape steve »

Why not paint the bottom if you are leaving it in the water for such an extended period? Seems like that would be less work. I store my boat on a trailer between use but have it in the water for 2-2.5 week stretches, at the end of which it is scummy and little (tiny) barnacles are starting to become evident. Probably not enough to alter performance but enough to be a pain in the butt to clean off (I use a scrub brush). I scrub the hull between use and get it pretty clean with some effort.

I have been thinking about getting bottom paint put on to make my life easier and reduce the need for scrubbing. Actually I have been thinking about getting the whole hull painted since the nyalic is so susceptible to getting dinged up. The main thing that holds me back is that I have the feeling the boat guys on the east coast probably dont have much experience painting aluminum.. I have seen a couple moored boats around here that have bottom paint
BroadCove
Posts: 47
Joined: Mon Jan 14, 2008 12:40 pm
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Location: Casco Bay, Maine

Re: Real World Performance Numbers

#4

Post by BroadCove »

Cape Steve - I have been thinking more about painting the bottom. One thing holding me back has been that one of my (many) reasons for going alloy was because I didn't *have* to paint the bottom. I beach the boat frequently (15-20x per summer), so bottom painting would be an annual event for me. Partly it's the expense (esp. if I pay someone else), and partly it's the hassle (if I do it myself). I spend about four hours a year with the pressure washer cleaning it now. I'm thinking of investing in a better commercial-style pressure washer instead of bottom painting. That would cost me about the same as painting the boat the first time, and I tend to get a good bit of use out of my current pressure washer for other things. We'll see how I feel come next spring!
BroadCove
Posts: 47
Joined: Mon Jan 14, 2008 12:40 pm
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Location: Casco Bay, Maine

Re: Real World Performance Numbers

#5

Post by BroadCove »

Got the boat back in the water last weekend and came up with the following performance numbers. I thought this would be interesting for any non-alloy owners considering an alloy boat. Given how I tend to run my boat (heavy), I think these numbers are pretty darn good from an efficiency standpoint and would compare very favorably to similar size NON ALLOY boats. I use/think in knots, so the numbers would obviously look about 15% better if converted into mph/mpg.

Boat: 26' Pacific HT, Suzuki 250 w/ 3 blade 15.25 x 19 prop
Load: 130 gals. fuel, 2 adults, 6 kids (9 - 15 yrs.), 4 dogs (large, medium and two puppies)
Bottom: Clean!
Conditions: Air temp 68F, water temp 63F, light chop
4000 rpm: 21 kts @ 9.5 gph (2.2 kts/g)
4500 rpm: 25.5 kts @ 11.3 gph (2.3 kts/g)
5000 rpm: 31.2 kts @ 15.5 gph (2 kts/g)
5500 rpm: 34 kts @ 19 gph (1.8 kts/g)
5850 rpm (WOT): 36.3 kts @ 21.2 gph (1.7 kts/g)

There's a sweet spot around 4700-4800 rpm where the boat/motor seem to run best. I didn't record that number, but it's around 28 kts at just over 12 gph. The motor "sounds" good at that rpm.

The load and sea state were about the same as the last time I was out; a clean bottom made a big difference.
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