Measurement Practice

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Paul Scott
Posts: 78
Joined: Sat Jan 31, 2004 5:56 am
Location: USA

Measurement Practice

Post by Paul Scott » Tue Feb 04, 2014 3:19 pm

I've been asking how canoes are measured over on Dinghy Anarchy, and it was suggested that I post over here. Over on Sailing Anarchy I go by Amati (that's the sloop in my avatar).
I live in the Inland Northwest of the US of A.

I'm the guy who posted the canoe with the planing shoe, but whether it is legal led to some questions about how the measuring tape is deployed.

So far I have been told that the athwartship tape is measured at the single nominated BMS, from one spot on the centerline.

How is the longitudinal tape used when measuring? Does it move?

Even if the longitudinal tape does move from side to side centered on the athwartship tape, it looks like it will meet no hollows concavities etc, although it becomes a Fat Boy....

Phil S thought that merely having concaves inside of the box (the one around BMS 1M by 2M by 11") was forbidden, if I understood him correctly.

So 2 questions from different areas of these forums-

1- I don't think the planing shoe was contemplated when the rule was formed, but a wide hull seems to stress the rule in general. I think the planing shoe is within the spirit of a development class, but I thought I'd ask the question for measurers in particular- would you throw it out? For those of you that haven't seen it, it is a development of the Starboard Phantom 360 hull.

2- the shoe does beg the Wetted Surface debate- how significant is friction, esp given the design opinion that canoes are not planing machines? Does wetted surface friction preclude hulls wider than minimum? I built and sailed a 36" beam quick and dirty canoe to see if it might work, and I don't really know what it showed me (other than it was fun to sail), given that the nearest canoe is Chris Maas's, and it's 8-9 hours away.

Paul

Paul Scott
Posts: 78
Joined: Sat Jan 31, 2004 5:56 am
Location: USA

Re: Measurement Practice

Post by Paul Scott » Tue Feb 04, 2014 3:55 pm

Boy did I mess up the Starboard board- it's the Phantom 377 Batwing
"Exuberance is better than good taste" -Flaubert

Steve Clark
Posts: 165
Joined: Fri Aug 01, 2003 2:26 pm

Re: Measurement Practice

Post by Steve Clark » Tue Feb 04, 2014 4:28 pm

Paul:
I find this confusion puzzling. That is one of the best sentences ever.
How it is supposed to work.
You identify the Beam Measurement Station.
In the olden days this was the 1/2 length of the hull, but now it is somewhere in between 1300 and 2300 forward of the stern. At this one station the hull has to satisfy the minimum beam and sheer height requirements. The tight tape rules are to assure that the designer did not meet these requirements by locally distorting the hull shape and thus circumventing the intent of the rule.
At the BMS a 1 meter tape is stretched athwartships (IE perpendicular to center line and water line) and should bridge no hollows greater than 1mm. If the boat was minimum beam and minimum freeboard, the outer end of the tape should end up comfortably below the gunwales at the BMS. If the boat is 1m wide at the 100mm waterline, the tape will end on the bottom panel. This tape is not moved fore and aft on the hull.
The 2meter fore and aft tape is centered on the stretched more or less parallel to center line and is swept along the hull. to assure that there are no fore and aft distortions for the sole purpose of satisfying the BMS conditions.
If the tape wraps over a chine, it should be able to do so without catching air.
In practice this is a simple test.
The problem with all these hull shape rules is that the designers quickly try to trade off the cost of the distortion against the benefit of a hull which is narrower tan the rule intends. So in many ways all you do when you write these things is tell the designer what shape bump you will accept. I figured a 2m long bump on a 5meter long hull was big enough to assure that the minimum beam and sheer height rules would be forced into the whole hull shape instead of bogged on.
I hope this clarifies.
SHC
Beatings will continue until morale improves

SteveC
Posts: 548
Joined: Fri Dec 22, 2006 10:32 pm
Location: United Kingdom

Re: Measurement Practice

Post by SteveC » Tue Feb 04, 2014 4:40 pm

Welcome to the forum Paul and there you go, the confirmed definitive answer from the man himself.

To be fair Steve, he was given some confusing advice on Sailing Anarchy.
Steve Clarke (UK)
GBR338 "Money4Nuffin

Paul Scott
Posts: 78
Joined: Sat Jan 31, 2004 5:56 am
Location: USA

Re: Measurement Practice

Post by Paul Scott » Tue Feb 04, 2014 7:57 pm

So as long as external chines are outside the reach of the 1m tape I'm good!

Thanks Steve-
"Exuberance is better than good taste" -Flaubert

Alistair
Posts: 243
Joined: Mon Sep 22, 2003 7:28 pm
Location: United Kingdom

Re: Measurement Practice

Post by Alistair » Tue Feb 04, 2014 8:12 pm

Hi Steve,
just to clarify what you intended, the 2m tape sweep is not limited by the 1m transverse tape, as it says in the rule, the 2m tape is centered on the bms not the tape, so the 2m tape goes right up to the gunnel, that's what I have always assumed.
Thanks
Alistair

Paul Scott
Posts: 78
Joined: Sat Jan 31, 2004 5:56 am
Location: USA

Re: Measurement Practice

Post by Paul Scott » Tue Feb 04, 2014 9:21 pm

What does the 2m tape do when it goes around a chine? Does it fold? Crease? Go straight out into space?

(I worked on a response for 2 hours and I still don't understand where the end of the 2m tape goes- like with a 30" beam square chine hull, where does the 2 m tape go at the chine, just before the 1 m tape goes around the chine and up the side of the hull?)

Alistair- you almost imply that the 2 m tape is centered on BMS on the centerline? -like it's the fulcrum of a the 2 m tape as a radius arm?
"Exuberance is better than good taste" -Flaubert

Paul Scott
Posts: 78
Joined: Sat Jan 31, 2004 5:56 am
Location: USA

Re: Measurement Practice

Post by Paul Scott » Tue Feb 04, 2014 9:23 pm

We need pics....
"Exuberance is better than good taste" -Flaubert

SteveC
Posts: 548
Joined: Fri Dec 22, 2006 10:32 pm
Location: United Kingdom

Re: Measurement Practice

Post by SteveC » Tue Feb 04, 2014 9:49 pm

Well actually looking at Steve's answer again, I'm concerned as I only focused on the the original question on Anarchy which was about the transverse tape and this is agreed to be fixed.

I can now see that the 2m tape measurement is a problem and is very ambiguous as it only says it should be centred on the BMS. I have assumed and I agreed this with Colin that this is only measured on the centre line of the boat. If the intention was to check everywhere it should say so and include a phase like "everywhere across the width of the boat from gunwale to gunwale parallel to the keel line".

Paul Scott
Posts: 78
Joined: Sat Jan 31, 2004 5:56 am
Location: USA

Re: Measurement Practice

Post by Paul Scott » Tue Feb 04, 2014 10:33 pm

I couldn't post pics here, but Canoe Anarchy in Dinghy Anarchy let me, so If you go over to the IC page there you'll see it more succinctly than my prose can manage
"Exuberance is better than good taste" -Flaubert

Steve Clark
Posts: 165
Joined: Fri Aug 01, 2003 2:26 pm

Re: Measurement Practice

Post by Steve Clark » Tue Feb 04, 2014 11:20 pm

Working on it.
Hope to be able to publish a PDF, I may need Jim's help.
SHC
Beatings will continue until morale improves

Paul Scott
Posts: 78
Joined: Sat Jan 31, 2004 5:56 am
Location: USA

Re: Measurement Practice

Post by Paul Scott » Wed Feb 05, 2014 2:46 pm

Why not define the 2m tape as a section of a buttock line?
"Exuberance is better than good taste" -Flaubert

Steve Clark
Posts: 165
Joined: Fri Aug 01, 2003 2:26 pm

Re: Measurement Practice

Post by Steve Clark » Wed Feb 05, 2014 3:49 pm

Because it doesn't just follow he butts. After it turns the bilge it becomes "waterlines" except that it isn't necessarily parallel to the DWL. The sheer height does not have to be the same across the 2 meter span, so the tape will angle a bit as if you were sanding with a long board.
Working on the diagram.
SHC
Beatings will continue until morale improves

colin brown
Posts: 85
Joined: Tue Aug 12, 2003 12:29 pm
Location: United Kingdom

Re: Measurement Practice

Post by colin brown » Sun Feb 09, 2014 6:33 pm

As the Uk Chief Measurer, it may assist if I clarify how the rule is interpreted in the UK.

The intention of Rule 5e ( the two tapes etc.) was to check the hull and prevent any hull 'bumping' or similar distortions so as to produce a narrow/thinner or similar hull.
In the UK we now have at least 5 different designs in production from moulds plus several owner designs.All of these designs have generated good clean canoe lines without any tricks and most are at the minimum end of the tolerance allowed.
All the UK canoes are measuredin the same way under rule 5e.
First the BMS is defined ( this can be anywhere the owner may choose within 1300mm and 2600mm of the stern). The position is marked on the underside of the hull on the centreline of thr rocker as a single point.
Next a 2m tape is centered on this point and laid along the centreline . 1m of the tape pointing towards the bow and stern and pulled tight against the hull. The hull is checked on this line line for hollows.( the tape is not rocked, rotated or otherwise moved.)
Next a 1m tape is centered on the BMS point on the rockercentreline, with 500mm laid transversely and pulle tight against the hull skin. The hull is checked on this one line for hollows. ( the tape is not rocked, rotated or otherwise moved.)
Any hollows are measured and must be less that 1mm.
Phil Morrison( a well known UK designer) has the same interpretation of the rulesas the UK committee. My instruction to UK measurers is that any other hull distortions , bumps, lumps, etc. are reported to the UK committee and are considered under Rule 3 'Spirit of the Rules' continued,................
colin brown

colin brown
Posts: 85
Joined: Tue Aug 12, 2003 12:29 pm
Location: United Kingdom

Re: Measurement Practice

Post by colin brown » Sun Feb 09, 2014 6:41 pm

Continued.............
Any difference in measuring methods and possible interpretations should be considered at the skippers meeting at the Worlds in September.Then if necessary the ICF can draw up any proposed rule changes or issue instructions to measurers to clarify the position to ensure that the intention of this rule is achieved.
Whilst the forum is a good way of exchanging ideas and information , it is better if clarification on rule interpretation is addressed through the Chief Measurer in each country, who can refer the matter to the ICF if necessary.
Colin Brown
colin brown

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