## Portuguese lorchas

### Re: Portuguese lorchas

I do not know in which period you are interested in?

### Re: Portuguese lorchas

No!, but that's not the question. If the dimensions are known then tonnage BM can easily be worked out.

OK, it was me, probably!

### Re: Portuguese lorchas

Not really, you have to obtain the same measurments.

At that time there were no united systems in Europe.

### Re: Portuguese lorchas

No, there are no unified system. But if basic measurments are known, length of keel and maximum width an approximation can be made which is probably good enough for wargaming.

If detailed dimensions are avaiable then an exact measurement can be obtained.

If detailed dimensions are avaiable then an exact measurement can be obtained.

OK, it was me, probably!

### Re: Portuguese lorchas

Probably not much help, but there are a few free to download recent Italian naval histories by Virgilio Ilari e Piero Crociani. If your Italian is up to it

http://archive.org/details/MuratsRoyalN ... 1806-1815/

http://archive.org/details/NapoleonsRoyalItalianNavy/

https://archive.org/details/NapoleonsLi ... y1797-1814

http://archive.org/details/MuratsRoyalN ... 1806-1815/

http://archive.org/details/NapoleonsRoyalItalianNavy/

https://archive.org/details/NapoleonsLi ... y1797-1814

OK, it was me, probably!

### Re: Portuguese lorchas

Thanks for the vindication, Cy. Also, I have the Radogna book and the three downloads already, but thank you for the info anyway.

Right, if you know the measurements of a foreign vessel, you can convert them into Imperial, then look up British vessels in the same class. You can then adjust the Imperial measurements to the British method of measuring. It's not for a serious history, it's just for getting as close as possible to the common tonnage method for wargaming purposes.

Right, if you know the measurements of a foreign vessel, you can convert them into Imperial, then look up British vessels in the same class. You can then adjust the Imperial measurements to the British method of measuring. It's not for a serious history, it's just for getting as close as possible to the common tonnage method for wargaming purposes.

### Re: Portuguese lorchas

*Storia della Marina da Guerra dei Borbone di Napoli*vols 1 and 2 contain little ship data of the type you are looking for. The 4th volume is expected to include this kind of detail in appendices. I do not know, however, when vols 3 and 4 might appear.

### Re: Portuguese lorchas

Thank you very much. I will anticipate vol. 4 coming out.

### Re: Portuguese lorchas

Volume 3 (dal 1830 al 1861)

Volume IV Appendice.

Volume IV Appendice.

### Re: Portuguese lorchas

Nothing to do with Portuguese lorchas, but concerning the discussion of calculating British builder's measure "tonnage" for non-British ships . . .

You don't need to compare dimensions with the dimensions of British ships if you have measurements that you can convert to British feet. The original British formula for burthen or builder's measure tonnage was (L × B × D)/94 where

L = length on gun deck measured from the outside of the stempost to the outside of the sternpost

B = beam measured from the outside of the planking

D = depth in hold

Later, ½B was substituted for D, so the formula became (L × B × ½B)/94.

"Inside" vs. "outside" was an important detail. The despicable Americans cheated by measuring INSIDE the stem and sternposts and INSIDE the planking (i.e., outside the ribs) and dividing by 95, and then publishing the results. This use of slightly smaller measurements and a slightly larger divisor gave their ships a smaller tonnage than they would have had if the Americans had used the correct formula, and thus defrauded British officers into thinking that the American ships were smaller than they really were.

In the case of Italian or other navies, it would be important, or at least useful, to know how the measurements were made. In the absence of information either way, one can, of course, assume that the measurements had been made correctly, outside the posts and planking. The bigger the ship, the less difference this makes in practice. Moreover, comparing burthen tonnage assumes identical lines, which might not be the case.

I often have to estimate displacement tonnage for ships of the 1740s for which it has not been calculated. At that time, the Swedish and French navies were actually calculating displacements. Jan Glete estimated the displacements of ships in other navies, to the nearest 50 or 100 metric tonnes, by reviewing plans and estimating "block coefficients," and this is what I do for ships of unknown displacement for which I have dimensions. I find a French or Swedish ship of known dimensions and displacement, or several, preferably of the same type (frigate, small two-decker, two-decked SOL, etc.) and calculate the volume of the prism defined by the average of gun-deck length and keel length × beam × depth in hold (data on drafts is available for French ships but I have not seen it for any others), for both the ship of known displacement and the ship of unknown displacement. I don't know whether the French and Swedes used "inside" or "outside" measurements and I don't usually know that for anyone else either, so I have to assume that they were the same. I then multiply the ratio of the volumes by the known ship's displacement. I try to do this for several comparison ships and usually get fairly consistent results. All of this assume that the lines, in terms of such characteristics as flat or rising floors and bluff or sharp bows, are about the same for both the ship being estimated and for the reference ships. So the formula for converting a reference ship's displacement to an estimate of the displacement for another ship is

(RV/EV) × RT = ET

where RV = the volume for the reference ship (whose displacement is known)

EV = the volume for the ship whose displacement is being estimated

RT = the displacement of the reference ship in metric tonnes

ET = the estimated displacement of the ship whose actual displacement is not known

Many of the French displacement figures are listed by Demerliac (I have not yet obtained a copy of Winfield and Roberts) as "environ X," introducing additional uncertainty. For that reason, I usually round everything to the nearest 100 metric tonnes. It's clear enough that 2400-tonne Spanish 70s and 2500-2800-tonne French 74s were significantly larger than 1700-tonne British 70s, for instance.

The French usually calculated or estimated

You don't need to compare dimensions with the dimensions of British ships if you have measurements that you can convert to British feet. The original British formula for burthen or builder's measure tonnage was (L × B × D)/94 where

L = length on gun deck measured from the outside of the stempost to the outside of the sternpost

B = beam measured from the outside of the planking

D = depth in hold

Later, ½B was substituted for D, so the formula became (L × B × ½B)/94.

"Inside" vs. "outside" was an important detail. The despicable Americans cheated by measuring INSIDE the stem and sternposts and INSIDE the planking (i.e., outside the ribs) and dividing by 95, and then publishing the results. This use of slightly smaller measurements and a slightly larger divisor gave their ships a smaller tonnage than they would have had if the Americans had used the correct formula, and thus defrauded British officers into thinking that the American ships were smaller than they really were.

In the case of Italian or other navies, it would be important, or at least useful, to know how the measurements were made. In the absence of information either way, one can, of course, assume that the measurements had been made correctly, outside the posts and planking. The bigger the ship, the less difference this makes in practice. Moreover, comparing burthen tonnage assumes identical lines, which might not be the case.

I often have to estimate displacement tonnage for ships of the 1740s for which it has not been calculated. At that time, the Swedish and French navies were actually calculating displacements. Jan Glete estimated the displacements of ships in other navies, to the nearest 50 or 100 metric tonnes, by reviewing plans and estimating "block coefficients," and this is what I do for ships of unknown displacement for which I have dimensions. I find a French or Swedish ship of known dimensions and displacement, or several, preferably of the same type (frigate, small two-decker, two-decked SOL, etc.) and calculate the volume of the prism defined by the average of gun-deck length and keel length × beam × depth in hold (data on drafts is available for French ships but I have not seen it for any others), for both the ship of known displacement and the ship of unknown displacement. I don't know whether the French and Swedes used "inside" or "outside" measurements and I don't usually know that for anyone else either, so I have to assume that they were the same. I then multiply the ratio of the volumes by the known ship's displacement. I try to do this for several comparison ships and usually get fairly consistent results. All of this assume that the lines, in terms of such characteristics as flat or rising floors and bluff or sharp bows, are about the same for both the ship being estimated and for the reference ships. So the formula for converting a reference ship's displacement to an estimate of the displacement for another ship is

(RV/EV) × RT = ET

where RV = the volume for the reference ship (whose displacement is known)

EV = the volume for the ship whose displacement is being estimated

RT = the displacement of the reference ship in metric tonnes

ET = the estimated displacement of the ship whose actual displacement is not known

Many of the French displacement figures are listed by Demerliac (I have not yet obtained a copy of Winfield and Roberts) as "environ X," introducing additional uncertainty. For that reason, I usually round everything to the nearest 100 metric tonnes. It's clear enough that 2400-tonne Spanish 70s and 2500-2800-tonne French 74s were significantly larger than 1700-tonne British 70s, for instance.

The French usually calculated or estimated

*two*displacements, one for just the hull and the other for the ship fully fitted out, with rigging, ordnance, ship's stores, water and victuals, and crew (even at just 150 lbs. each for a man and his personal effects, this is significant). I use the "full load" figure.