LR Rule Length......

Hello,

LR rules define the rule length as:
6.2.1. Rule length, LR, is the distance, in metres, on the summer load waterline from the forward side of the stem to the after side of the rudder post or to the centre of the rudder stock if there is no rudder post. LR is to be not less than 96 per cent, and need not be greater than 97 per cent, of the extreme length on the summer load waterline. In craft without rudders, the Rule length, LR, is to be taken as 97 per cent of the extreme length on the summer load waterline. In craft with unusual stem or stern arrangements the Rule length, LR, will be specially considered.

6.2.2. Length between perpendiculars, Lpp, is the distance, in metres, on the summer load waterline from the fore side of the stem to the after side of the rudder post, or to the centre of the rudder stock if there is no rudder post. In craft with unusual stern arrangements the length, Lpp, will be specially considered. The forward perpendicular, F.P., is the perpendicular at the intersection of the summer load waterline with the fore side of the stem. The after perpendicular, A.P., is the perpendicular at the intersection of the summer load waterline with the after side of the rudder post or to the centre of the rudder stock for craft without a rudder post.

May anyone tell what is the difference between LR & Lpp? How can I define LR for planing boat with outboard engines?

Thanks in advance

 

"...LR is to be not less than 96 per cent, and need not be greater than 97 per cent, of the extreme length on the summer load waterline. .."

There is your answer

 

Dear Ad Hoc;

I already noticed what you mentioned (LR<=97% load line) but how can I specify both of LR & Lpp for boat with outboard engines, it doesn't has rudder stock or post; I this case can i consider Lpp=LWL ?

could you please draw a sketch for this case & specify Lpp, LWL, LR?
Should I consider LR as an absolute figure that can't be specified on a drawing?

I read in on of your posts that your are LR Tech Committee member, hope you could help me in this regard.

Thanks

 

You're getting confused for the very obvious reason, LR rules, like all, are based around the hull envelope and what is inside it, or protruding from it. If your engine is an outboard, the above assumptions do not apply, ergo one defaults to the easiest:

"...LR is to be not less than 96 per cent, and need not be greater than 97 per cent, of the extreme length on the summer load waterline. .."

Ask yourself this Q...what is the definition of LWL and what is the definition of Lpp....just look in any naval arch book if you're not sure. QED.

When you run the numbers of 96% and 97% on a small boat, you'll then realise it makes zip difference which value you select. In other words the prescriptive rules that you are using have values which are really outside the scope of the parameters for said rules.

 

I agree eith this

 

Meebo

Yes, I am on LR's Tech Committee.

Lpp, is simple, length between perpendiculars.
Lwl, length on the waterline; for almost every design, is the same as Lpp
LR, is just a fudge factor for LR calc's. (From big ship stuff)

So, if you can't ascertain the LR, just use, not less than 96 per cent, and need not be greater than 97 per cent of Lpp/LWL. The difference is minor on 'smaller vessels'.