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Old 06-15-2015, 10:50 PM   #21
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When I bought my Celica GT4, I knew I didn't need 155kw (about 200hp) and a top speed of 240kph, (=~150mph), but I felt that was it was designed as a rally car, with all that implies, then if I just drove it sensibly, it would not even be breathing hard in normal use, and should be bullet-proof. This philosophy has been proven correct. I still love it and it's still going strong 25 years later, in near perfect condition at 270,000 km, (=~, oh bugger it, you do the damn US math).

Anyway, I sort of feel that boats are not that different. As I have on occasion been darned glad of the extra power to get me out of trouble, (and on occasion, as it is 4WD), tow someone else out of trouble, so also am I glad that my boat at hull speed is not really breathing that hard, has reserve, and on occasion I have actually used this to tow other grounded boats off. As I see it, as long as it's up to operating temp, further load is largely irrelevant, and it is so frugal I don't mind buying the bit extra fuel for that reserve. The fact it is still effective purring, and 'using no oil', (I know - they'll use a bit - gotta, right), at some 5000 hrs plus, I think I'm not far wrong - just saying'.
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Old 06-16-2015, 07:17 AM   #22
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Hope everyone in the discussion understands the difference between displacement weight and documented gross tonnage....they can be quite a bit different.


http://www.uscg.mil/hq/msc/docs/CG-5397.pdf


http://www.qualitymaritime.info/Pres...mplified_0.pdf


Definitions from Wiki....but the above shows the diff....


Tonnage is a measure of the cargo-carrying capacity of a ship. The term derives from the taxation paid on tuns or casks of wine, and was later used in reference to the weight of a ship's cargo; however, in modern maritime usage, "tonnage" specifically refers to a calculation of the volume or cargo volume of a ship. Tonnage should not be confused with displacement, which refers to the actual weight of the vessel.
Measurement of tonnage can be complicated, not least because it is used to assess fees on commercial shipping.
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Old 06-16-2015, 08:07 AM   #23
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Thank you Scott,
I suspected as much.

We're up early for a road trip to get a new trans oil cooler so not much time.
So for our purposes tonnage numbers have no value. Would be nice to know what Early Spring weighs but I don't think it will come to pass. In this case guessing is probably about as close as we'll come.

I tried to find some comparable boats w displacement numbers but didn't do well at all.

For me I'd do well to study QB and dannc's previous posts and see if I can learn more. Anyway when I said "WAY" over powered I a bit off or more and I WAS WAY off re Duwam's size. However I do think Early Spring would be better served w a 3-53.

QB wrote "Eric, displacement goes like length cubed. (33/30)^3 * 8 = 10.6 tons." My guess for Early Spring's weight was 10 tons. Maybe I was not far off. My estimate for Willy's power requirement is 30 to 33hp. I put 40 in her and it seems very close to ideal. That's 5hp per ton. Skeene says 44hp. Dan's conclusion of 50hp seems extremely correct but w my own experience I finally decided I could actually do w 6 to 8 hp less. But if I repowered again would I have the guts to go to 4lbs per hp (33 for Willy) ..... probably not.
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Old 06-16-2015, 10:34 AM   #24
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Originally Posted by psneeld View Post
Hope everyone in the discussion understands the difference between displacement weight and documented gross tonnage....they can be quite a bit different.
This is true. Also USCG and Transport Canada rules for measuring gross and net tonnage are somewhat different, and here we are comparing a US and a Canadian boat.
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Old 06-16-2015, 10:50 AM   #25
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This is true. Also USCG and Transport Canada rules for measuring gross and net tonnage are somewhat different, and here we are comparing a US and a Canadian boat.
fair enough...just a reminder for those that didn't know that for US vessels...

Do you have a link for Canadian Vessel measurement so I can compare the calculations?


One quick glance at one source showed the measuring to be similar as it is about volume vesus weight....


http://wwwapps.tc.gc.ca/wwwdocs/Form...408-10_E_X.pdf
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Old 06-16-2015, 01:34 PM   #26
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Hope everyone in the discussion understands the difference between displacement weight and documented gross tonnage....they can be quite a bit different...
Hobo has a design displacement at 1/2 load of 17.63 tons and her gross tonnage is 36 tons and her net tonnage is 29. When we were overseas on our last boat, sometimes port fees were calculated on the net tonnage and in our case it wasn't very much.
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Old 06-17-2015, 11:04 AM   #27
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One quick glance at one source showed the measuring to be similar as it is about volume vesus weight....http://wwwapps.tc.gc.ca/wwwdocs/Form...408-10_E_X.pdf
Yes and the corresponding simplified US method is here: http://www.uscg.mil/hq/msc/tonnage/d...-1_Current.pdf. They use different shape factor coefficients, account for above-deck structures differently, etc.

Then there are various non-simplified formal tonnage measurement schemes that have been used in the past. These days the US and Canada are supposed to be following the International Convention on Tonnage Measurement of Ships and large commercial vessels' measurements should be updated to that by now, but not necessarily for smaller boats.

You are right that all these tonnage measurements are volume based and don't actually involve weighing the vessel. Since a floating boat's displaced volume of water equals its weight, one might hope that they should be comparable, but that is not often the case.
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