LR rule length>>>>help

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

 

"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."

"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."

In my opinion Lpp is equal to the designed hull waterline length and LR 97% of that, for an outboarded boat. But to be more sure, you can ask Lloyd's (rules@lr.org)

Or then:
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T +90 (0)216 368 9930
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E istanbul@lr.org


Cheers.

 

Thanks for your input, I agree with you. Anyway I'll contact LR.

 

A little late on the reply here, but I am new as well.

The rule length prevents a ship with a rudder in an extreme position from being considered, for the sake of the rules, at a length which is not reflective of it's "true" (waterline) length. This is the 96%/97% rule. For most ships, this will be, essentially, the Lpp anyway.

I believe the Lpp entry exists more to define the location of the FP and AP.

Wondering if you had a clarification from LR?

 

Not sure which of Lloyds register rules you are looking at.
In the Rules for Yachts and small craft L is just the average of LOA and LWL.

 

I don't have LR rules for yachts & small craft, the above defintions are for special service vessels, I checked BV rules for yachts and I found:
3.2 Rule length

The rule length L is equal to LWL where LWLis the waterline length measured with the yacht at rest in calm water, at the full load displacement.

3.3 Hull length

The hull length LHULL is equal to the total hull length, from the extreme foreward part of the hull, excluding any outfitting protusing, and the extreme aft part.

3.4 Ends of rule length LWL and midship

3.4.1 Fore end
The fore end (FE) of the rule length LWL(see Fig 1) is the perpendicular to the full load waterline at the forward side of the stem.



3.4.2 Aft end
The aft end (AE) of the rule length LWL (see Fig 1, is the perpendicular to the full load waterline at a distance LWL aft of the fore end.



3.4.3 Midship
The midship is the perpendicular to the waterline at a distance 0,5LWL aft of the fore end (see Fig 1).