Thinking about building a bay boat

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fallguy1000
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Re: Thinking about building a bay boat

Post by fallguy1000 »

I've not read the standard, but looked at the calc.

Calc for remote steer is different than tiller..

Factor in feet
22•8.5=187

Remote steer uses multiplier of 2 less 90

2•187 = 374

374-90 = 284 hp

The HP rating you cited is for tiller.

Of course, this formula is a simplified method that does not account for the hull. So don't go using it anyone!
BarraMan wrote: Thu May 18, 2023 1:44 am I am NOT a naval architect! 8O and I am confused. :doh:

If I use the Australian design standard at the time I built my boat, AS 1799-1.2009, which I understood at that time to be essentially the same as the USCG/ABYC standard, to calculate the recommended max hp for my boat (MG20 x 1.1) I come up with 269 hp - rounded out to 270 hp! Jacques specified max hp for the MG20 as 250 hp, so in the same ball park. I went with 250 hp for my up-scaled MG hull cause I figured that was heaps for my purposes and matched the Yammy 250 Vmax SHO that I had in mind for my build.

While the PH22 is a different design from the MG20, the dimensions for the calculation of recommended max hp as per AS 1799 are essentially the same as for my hull, so AS 1799-1.2009 would suggest 270 hp max. Interestingly, Jaques recommends 150 hp max for the PH22, although he does say that the USCG/ABYC specs would indicate more. I assume that his recommendation is based on the style of the hull and the specified scantlings and glassing etc.

However, if I use what appears to be the latest AS 1799 (USCG/ABYC) standard (AS 1799-1.2021) the calculation comes out as 125 hp for both boats.

Something seems wrong here! :doh:

While 125 hp may come close to Jacques recommended max 150 hp for the PH22, my boat with 125 hp would be a 'dog'! My boat handles the 250 hp with ease and would be quite happy with 300 hp. On the other hand, the PH22 with 250-270 hp would be a beast! :help:

The other test for determining max hp specified in AS1799 involves running the hull through a 90o turn at max speed within set dimensions. I am pretty confident that my boat would pass this test - but I am equally confident that a PH22 with 250 hp would fail. I think the PH22 would power slide, or worse, outside the required specs! :help:
The maximum horsepower capacity must be computed as follows:
(1) Compute a factor by multiplying the boat length in feet by the maximum transom width in feet
(2) Locate horsepower capacity corresponding to the factor in Table 183.53.
(3) For a boat with a factor over 52.5, if the horsepower capacity calculated in Table 183.53 is not an exact multiple of 5, it may be raised to the next exact multiple of 5.

Table 183.53—Outboard Boat Horsepower Capacity [Compute: Factor=Boat Length X Transom Width]
If factor is over 52.5 and the boat has remote steering and at least 20″ transom height, horsepower capacity is (raise to nearest multiple of 5) = (0.8 X Factor) −25
So, [0.8 x (22' x 8.5')] - 25 = 124.6 hp

Am I going wrong somewhere? :doh:
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Browndog
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Re: Thinking about building a bay boat

Post by Browndog »

Thanks guys for the variety of suggestions. Adding a layer of 12 oz biaxial inside and out seems like a relatively small thing to accommodate the 200 hp motor especially since I was already thinking that an extra layer would be needed on the interior under the fuel tank anyways.

Now to spice things up a bit.

I’m a big fan of Carolina style boats and the bow flare of the CS 23 & 25 in particular. The GS 28 X with optional flared bow is kind of what I’m thinking. I also really like the look of the tumblehome at the stern of the CS 23 & 25 and the RB 18.

If I wanted to incorporate some tumblehome to the stern and some flare to the bow besides changing the shape at the top of the frames and transom and cutting slits in the plywood hull and side plankings, anything else to consider?

Not wanting to change the bottom running surface or the sheer line, just the top side cosmetics.

What do y’all think?

fallguy1000
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Re: Thinking about building a bay boat

Post by fallguy1000 »

I would make a mould and strip plank those sections. Slitting is going to be a crap shoot and the strength is gone then anyway.
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BarraMan
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Re: Thinking about building a bay boat

Post by BarraMan »

How did we get from a PH22 to a flared bow and a tumble home stern? :doh:

fallguy1000
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Re: Thinking about building a bay boat

Post by fallguy1000 »

BarraMan wrote: Fri May 19, 2023 9:31 am How did we get from a PH22 to a flared bow and a tumble home stern? :doh:
The great fallacy of flared bow is that the boat will be drier, but my tiller skiff is a wet ride and it all happens way after any bow flare would help. The thing that helps is a helm station.

Try it when the water is 40 degrees. It'll wake you up.
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TomW1
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Re: Thinking about building a bay boat

Post by TomW1 »

I would say no to the flared bow, just not enough space to make it look good. Then build a model of the tumble home to see how it would look and if you like it go for it. You could also model the bow to see if I'm all wet on that. There are some boats that look good with what you want to do others not so much and others don't perform well a flared bow as pointed out already.

Tom
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

Fuzz
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Re: Thinking about building a bay boat

Post by Fuzz »

For a man with your proven boat building skills it should be no problem. I say go for it, after all that is part of why we build boats ourselfs.

Browndog
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Re: Thinking about building a bay boat

Post by Browndog »

The suggestion to build a model with the modifications that I have in mind is a great idea!

Not thinking about the Carolina flare for spray reduction. The plan is to add spray rails and/or reverse chines to keep the spray in the bay. I just like the way it looks. Not planning on going crazy with the flare. I think that the optional flare on the GS 28X is just about perfect.

The PH 22 as is just looks a little pointy and narrow to me at the bow compared to the FS 19 which has more of a vertical look to it. That is one thing that makes the FS 19 so nice and why it feels like a bigger boat. If Jacques had extended the keel and shear line of the FS 19 at the bow it would have had a much pointier bow, added a couple feet to the overall length, but not really produced any more useable deck space, useable storage space or lengthen the running surface.

The PH 22 has a completely flat shear line while the FS 19 has a slight upward curve to it. The overhead view also shows that the PH 22 is widest at the transom whereas the FS19 while not having any tumblehome is widest further forward so it narrows a little bit in the rear which gives a similar visual effect as tumblehome.

I think that I can handle the frame and transom modifications to achieve the look that I prefer. The small amount of flare that I’m thinking could probably be handled via slits. The strip planking suggestion is a good alternative though.

Keep the suggestions coming!

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