Small Pahi Group

Comment by Alex on January 6, 2013 at 6:07am

Tama Moana being the pahi upgrade - narrower, less rounded hull/ shorter lwl for length - more rake to the bow and stern/ bigger rudders. But limited accommodations and none possible in a smaller size, without superstructure.
Pity we have to fit people in - there'd be a lot less compromises.

Comment by Galway Bay on January 6, 2013 at 10:47am

Alex - Apologies for taking so long but here is the proa. Definitely is a Pahi so it is at home here. Looks like a P31 main hull with a shorter cabin and only two crossbeams. From your photo it seems the prototype was not as drawn here. Seems they used an existing P31 hull.

The experience of "JZERRO" etc. seems to show that a leepod is an essential part of a cruising proa as a last source of righting.

It has been posted here that this boat capsized and JWD lost interest. Also at this time the Tiki range was being created and occupied all their time so that the older designs were left to one side.

I love the idea but when you start including leepod etc. the design starts to increase in complexity to near a bridgedeck boat.

One idea I have never seen used for the reversing rudder problem would be two spade rudders with the forward one allowed to rotate through 180 then simply locked fore/aft as a daggerboard while the aft one does the steering. No tricky lining-up so that it can be lifted. No case to build.The underwater profile would be identical to what I have with my board down and I know that works. Drawback would be a fixed draught of 30" [ 700mm ] or so.

Comment by Alex on January 6, 2013 at 4:45pm

Thanks for the pic. The text is funny. Pity he didn't stick with the proa concept.

Comment by Alex on January 27, 2013 at 4:30am

Hi. Galway (or others) can you tell me the p31 waterline beam? Or WLL/WLB ratio? Thanks.

Comment by Galway Bay on January 27, 2013 at 7:19am

At 1.5 ton [empty] 550 /22" on a draught of 420 /17". 

At 2.0 ton 750 /30" on a draught of 490 /20".

So the ratio [empty] is 13.4 : 1

These are as given on my general arrangement sheet. This tallies with my own measurements for painting the a/foul. ie. 600 /24"measured on the side panel.

I had never really considered this before and just had to do some calculations. The draught is so low I felt the displacement must be wrong. Right enough applying the fairly full Prism./Co . of 0.6  I came up with a disp. of only 1 ton. I have never weighed my boat but from experience of towing I believe the 1.5 ton is closer to the mark. So like any lazy schoolboy I set about "cooking the books" to get the answer I wanted. Casualty No, 1 was the Prism./Co. The mid sections in the Pahi 31 have no taper or rocker at all so there disp is simply crossection x length. The bow / stern taper [obviously!!] and trhe Prism./Co. of 0.6 seemed appropriate here. Add it all up and there I had it - the magical 1.5 tons !!

However never one to let good enough alone I worked backwards from this displacement to get a Prismatic Co. for the design as a whole - a staggering 0.88 !! 

This all ties in with my experience ie. a great load carrier that gets up to 8kn easily with little wake and is good in waves [no pitching] but starts to drag a marked wake at 10kn.  A top class sea-cruiser.

J.W. has recommended the Pahi 31 as the minimum boat he recommends for ocean crossing [ wnile recognising that others have used smaller].

 

 

Comment by Alex on January 27, 2013 at 10:11am

Thanks. Wow cp is high - I guessed it at 0.78 or so.....
So fully loaded WLL/WLBr is 10.13 (at advertised WLL of 7.60m)?
I don't suppose you'd know the WLB of the P42 ?

Comment by Galway Bay on January 27, 2013 at 11:01am

Sorry no for 42. My figures above for P./C.are only "Guesstimates" based on assumed weight etc. Still they do fit in with my experience of the boat in a general way. Interesting that I calculated what it would take to put her down 24" /600mm and it is 2.4 tons ie. a full ton of loading. I think she could carry this 'tho I have never tried. You would still have good freeboard with 24" / 600mm clearance under the cockpit and 36" /900mm under the fore deck. Some of the more "modern" designs cannot match this even when empty ??  She is also far more stable than some of similar size all in all well suited to long passages.

Comment by Alex on January 27, 2013 at 11:50am

I know the original pP31 was 35' - why then did they reduce it to 31'?
Why isn't there an intermediate, as with the Tiki range, such as a Pahi 36/38?
Similar to, say the Tama Moana?

Comment by Alex on January 28, 2013 at 3:53pm

Sorry to be a pain ... But WSA for the P31 ? I'm trying to put together some performance figures.

Comment by Galway Bay on January 29, 2013 at 1:00am

Pahi 35 - I cant speak for JWD and while I saw the 35 it was a long time ago. As I remember it the 31 [from memory !!] is a "compressed" 35 ie the same crosssections with reduced spacing. That is the 35 is not really a seperate boat but a stretched 31. A 35 should really include extra head / elbow room not just extra length. The 35 was designed remember specifically for the Round Britain Race where low narrow hulls [for their length] might be seen as an advantage. On a cruiser the head / elbow room is perhaps more appropriate to a boat of about 30ft.

This is all guesswork based on possibly flawed memory.

The success of the Tiki seems to have put the Pahi range on the backburner for a long time. Comments at the time show that James realised the 31 needed a Mk11 [this boat is overbeamed etc.] but this was never done.

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