ISO 12217-3 simplified offset-load test

[TANSL]

 

[mc_rash]

The coloumns "kg*m" are LCG*mass, TCG*mass, VCG*mass from which the sum is calculated. The sum of moments divided by sum of masses results gives the total LCG, TCG and VCG of the loadcase. They do not effect anything in the whole sheet they are just there to calculate the CoG.

 

[TANSL]

Okay, you're right, I haven't explained well what I wanted to clarify, but, if you don't mind, check that in the graphs you enter the heeling moments and the righting moments in the same units. On your ordinate axis the values of the moments are given in N.m and, as I believe, Maxsurf gives you the values in kg.m. That is, on the graph you have to place the values obtained from Maxsurf multiplied by 9.81.
If I am wrong, please excuse my insistence.

 

[mc_rash]

From the Maxsurf results I use the GZ (m) values multiplied by mass*g (in this case 421kg*9.81 m/s2). I could have used the righting lever calculated by Maxsurf and multiplied only by 9.81, the results still would be the same. Later when I'm home I will re-check the units but I'm 99.9% sure they are correct.

I did a quick full-procedure test in Maxsurf and the boat capsized with 2 loads equivalent to 85kg/person. If also the full procedure will fail with the reduced mass 85*L_h/6 my guess is I will have to follow option 3 (power <= 3kW, cat. 3) which does not require an offset load test bust must fulfill the capsize recovery test (I don't know wether this is possible to do by calculation or only by physical tests).

 

[gonzo]

I see a problem with the crew area. Your drawing shows there is no deck, so the crew area should extend to the edge. If you assume the crew is always sitting, there should be a permanent placard indicating that they can't stand. However, that may be an issue when boarding.

 

[mc_rash]

Hey @gonzo thanks for your replie.

I'm just in the begin of the design and I wanted a quick check of the rules which turned out to be not as quick as I wanted to. Regarding the crew area, see post #5, "Note 2". The design is an open boat, no deck at all so according to "Note 2" I guessed the crew area comprises of the whole boat area in planview (probably hull thicknes can be subtracted but since it's preliminary design I ignored a few mm's). Another question, see also post #5, the slope of inclined areas may be excluded of the "working deck" (which I guess is the same for pleasure craft and commercial "working" boats?) and the exclusion of "ledges" (I'm not native english, but I assume ledges might be something like a border). Until know I included the inclinend side surfaces and the "ledge". If the rules allow to exclude these values the breadt_crewarea would minimize to roughly 1.1 m which would lower the crew heeling moment (not enough but quiet a bit)

 

[gonzo]

Some years ago I did the simplified tests for some 30 foot cargo canoes we were building in England. My recolection is the asssumption was that the crew can sit to the end of the bench. There also was an assumed CG for the crew that could be used.

 

[TANSL]

@gonzo, simplified test can only be carried out by calculation.

 

[mc_rash]

The simplified method should be the same for boatlength < 6 and > 6 m but indeed as TANSL states it can only be done by calculation.

The simplified method has a greater safety margin, I guess the crew heeling moment has been derived from 98kg*9.81m/s2*CL*(Bc/2 - 0.2)*cos(phi) where Bc/2 is the half beam crew area subtracted by 0.2m (as peoples TCG cannot be closer than this sitting next to a boats side surface). This formula makes absolutely sense to me.

The full procedure also didn't pass. Are there any ideas how I can increase the righting lever?

 

[TANSL]

Lowering CoG, increasing waterplane inertia or reducing displacement.