Steve's PH22

To help other builders, please list the boat you are building in the Thread Subject -- and to conserve space, please limit your posting to one thread per boat.

Please feel free to use the gallery to display multiple images of your progress.
fallguy1000
* Bateau Builder - Expert *
* Bateau Builder - Expert *
Posts: 10199
Joined: Tue Jan 12, 2010 12:25 am

Re: Steve's PH22

Post by fallguy1000 »

Did you buy the core?

The core might need to be made from thicker materials for 250hp. For all that speed, you need a stiffer bottom and foam core and others use the cube rule. So, for any bottom, core A versus core B works as follows.

Thickness of Core A stiffness is X

Core B is raised to 3rd power to get stiffness

So, for example.

A 1" core is stiffness X.
A 2" core is 8 times stiffer.

Or for a 1/2" core, a 3/4" core is 1.5^3 or 3.375 times stiffer.

Yes, it can be done with fiberglass, but epoxy, glass, weight, money are the cost..

Now, I saw what happened here on the thread with all the other business, so I won't say more, but the foam thickness needs some discussion and I offer this as a friendly conversation starter with the designer; nothing more.
My boat build is here -------->

viewtopic.php?f=12&t=62495

OneWayTraffic
* Bateau Builder *
* Bateau Builder *
Posts: 1663
Joined: Sat Jan 10, 2015 7:13 pm
Location: New Zealand

Re: Steve's PH22

Post by OneWayTraffic »

Stiffness of a single skin scales as the cube, sandwich panels scale as the square of the core or separation between skins. If you recall Calculus this should make sense as the Integral of the square is a cube. The cores integral stiffness scales as a cube, which matters for ply, but since nearly all the strength is in the skins, that scales as a square.

There's a discussion on this on page 6 of the Diab handbook. I'd never build from foam core when ply is cheaper, but I'm one of those that enjoys reading formulae.
http://www.stmboats.com/articles/sandwich_hb.pdf

Steve your comments on HP and the speed you want out of your boat make sense. I'm happy at a much lower speed; that style of tourney fishing is not a NZ thing.

fallguy1000
* Bateau Builder - Expert *
* Bateau Builder - Expert *
Posts: 10199
Joined: Tue Jan 12, 2010 12:25 am

Re: Steve's PH22

Post by fallguy1000 »

OneWayTraffic wrote: Mon Sep 13, 2021 7:22 am Stiffness of a single skin scales as the cube, sandwich panels scale as the square of the core or separation between skins. If you recall Calculus this should make sense as the Integral of the square is a cube. The cores integral stiffness scales as a cube, which matters for ply, but since nearly all the strength is in the skins, that scales as a square.

There's a discussion on this on page 6 of the Diab handbook. I'd never build from foam core when ply is cheaper, but I'm one of those that enjoys reading formulae.
http://www.stmboats.com/articles/sandwich_hb.pdf

Steve your comments on HP and the speed you want out of your boat make sense. I'm happy at a much lower speed; that style of tourney fishing is not a NZ thing.
So, how does that work in my example for Steve?

Separation of 1/2" core versus 3/4" core is 1.5^2 or 2.25 times only versus my citation of 3.375? (For same skins)

Meaning a 1" core is 4 times stiffer than 1/2" core?

Building this speed demon from foam might require thicker foam and more bulkheads and even more long tees then.

I gotta read that Diab text because this is new to me. And I'm even more curious about the foam plan/layup.

Steve---how you build a foam bottom is really critical because if you have even small air pockets on the bottom; those pressures are rather significant at 70mph and the laminate can erode quickly. You can't allow them; fyi. Any air pocket must be ground or injected fully and then the injection site faired. I am not trying to beat any dead horses here. Just inform. I don't care how fast you want to go. I would even be looking at the shear ratings of various cores. You want something very high as a skin failure is certain in any lower shear foams. The shear rating of corecell M60 is about 100psi and the shear rating of M200 is over 400psi. I know from my reading that the shear must be addressed in go fast changes. (The water pounding forces are very high; no joke). What would happen if you build a beautiful hull with a low shear rating is it would delam from either a small impact or jist wav pressure and that delam would grow under hydraulics. Another reason to probably bag the job... The designer must do calculations of the shear demands and specify a core capable...I don't know those calcs, btw, jist that they are required.

Another thing to be very mindful of in designing a go faster boat is the engine weight/moment for the bigger engine. 100 pounds? added stern weight must be addressed. If the designer knows the center of mass, the moment of the additional weights are known and you MUST create offsetting moments or the boat will squat. That moment in a ph22 is probably ?900ft#s. Moving a 40# battery forward 2 feet is only going to give you an 80 ft# offset, for example. Moving weights forward can create a bending stress on the hull, but this may be addressed in a core thickness change or adding another stringer. Ultimately, the boat will need more weight moved forward.

Kindest regards. It is easy to sound like I am against the plan, but I am actually looking out for some true pitfalls for you.
My boat build is here -------->

viewtopic.php?f=12&t=62495

jacquesmm
Site Admin
Site Admin
Posts: 28215
Joined: Wed Aug 14, 2002 1:00 am
Location: Florida USA
Contact:

Re: Steve's PH22

Post by jacquesmm »

Wow, what a debate.

I was working on the "high" speed lamination schedule this week-end and did not visit the forum.

Let's clarify where we stand:
- I will give a lamination schedule for the PH22 with the specified max. HP in the study plans
- I state very clearly that 250 HP on a PH22 will be excessive and dangerous, this can be confirmed by the USCG rules.
- if a builder absolutely wants to build a foam cored PH22 for 250 HP, I will give optional "experimental" specifications, no guarantees.
- the building of such a boat will be much more complicated than a standard PH22 in foam. Many details will be different like centerline keel lamination, stringers on pads, chine and deck to sides seam etc. etc. It will require a different type of foam, different layup, different tabbing and I must create drawings for that. I am tempted to scan pictures of my text books and design manuals to save a couple of days of work. Because of copyrights, I will not post those scans but will email them to the builder.

It is my intention to redesign some of my boats for foam sandwich but I did not plan to design a foam cored PH22 for 250 HP.
For most boats, my current specs for foam sandwich are simple, the boats are easy to build. This one will be complicated and costly.
I will help the builder to end up with the best possible boat but I can not guarantee the result.
Jacques Mertens - Designer
http://boatbuildercentral.com

Matt Gent
Very Active Poster
Very Active Poster
Posts: 600
Joined: Sat Jan 05, 2008 7:54 am
Location: Treasure Coast, FL

Re: Steve's PH22

Post by Matt Gent »

Sounds like OP wants to build the PH22 like the Morejohn microskiffs. Lots of cool builds going on over there, but the weight and speed are in a different category.

And the 250hp desire is understandable, as so many production 22' bay boats can be powered that way. Frankly if I were going that path, I'd probably draw up (or commission) the design from scratch since you won't be limited by the plywood bend constraints.

Can't comment on the lamination, but I have rebuilt (re-cored) two speed boats, one for +/-80mph and one for 100+. I replaced the existing rotten butcher-block balsa core on the running surfaces with 5/8" Corecell A500. For two reasons - it is much tougher than the PVC foams, and the perforation is set up to vacuum bag it in place for good resin dispersion. I did use Divinycell H80 for bulkheads, stringers, seats - where they don't see the slamming and cyclic loads of the bottom, and are primarily a form for the glass skins. Hopefully you can find a use for the foam you have bought already.

fallguy1000
* Bateau Builder - Expert *
* Bateau Builder - Expert *
Posts: 10199
Joined: Tue Jan 12, 2010 12:25 am

Re: Steve's PH22

Post by fallguy1000 »

Matt Gent wrote: Mon Sep 13, 2021 1:17 pm Sounds like OP wants to build the PH22 like the Morejohn microskiffs. Lots of cool builds going on over there, but the weight and speed are in a different category.

And the 250hp desire is understandable, as so many production 22' bay boats can be powered that way. Frankly if I were going that path, I'd probably draw up (or commission) the design from scratch since you won't be limited by the plywood bend constraints.

Can't comment on the lamination, but I have rebuilt (re-cored) two speed boats, one for +/-80mph and one for 100+. I replaced the existing rotten butcher-block balsa core on the running surfaces with 5/8" Corecell A500. For two reasons - it is much tougher than the PVC foams, and the perforation is set up to vacuum bag it in place for good resin dispersion. I did use Divinycell H80 for bulkheads, stringers, seats - where they don't see the slamming and cyclic loads of the bottom, and are primarily a form for the glass skins. Hopefully you can find a use for the foam you have bought already.
I'll try to avoid extended debate and this is not a critique of your work Matt, but the problem with the a500 core is the interface between the bottom or top deck and the sides. JM will show the OP what to do, but what happens with an a500 core at the hulls edge is massive compression loading. Just think about it like this...instead of the a500 foam, put a neoprene sponge in place of the a500...it does fine until the sides of the boat press down on it. At that point, it is subject to massive crushing loads. So that interface requires special attention. So does the hull to deck interface for same reasons. The deck, in light(er) foam comes crashing down onto the hull sides which do not move and you can actually crush the foams. There are books written on these interfaces. The Skoota does not really need to consider these forces much because the boat is a wave cutter and not really supposed to jump waves, but go fast boats are subject to tremendous loads.

But an a500 bottom to hullside interface may not be sufficient. Again, only for the OP. Generally, a high(er) density core or a no core lamination occurs..but it gets far more complicated to build to avoid busting the boat at high speeds.
My boat build is here -------->

viewtopic.php?f=12&t=62495

jonnymac
Active Poster
Active Poster
Posts: 338
Joined: Sun Jun 21, 2020 8:33 am
Location: Eliot, ME

Re: Steve's PH22

Post by jonnymac »

I found some old timer marine surveyer’s website talk about this exact problem and his observations that is why so many of these balsa or otherwise cored boats had hull failures, was in the early days people didn’t know to consider these things small failures led to water intrusion then core failure completely as the absorbed water basically crushed the core every time the boat hit a wave. His observations where everything from sailboats to fast fishing boats. I’ll try and find the website.

edit: website is here https://www.yachtsurvey.com/core_materials.htm

Now what I didn’t appreciate was his attitude was basically because someone had bad design in the past means no one can do it in the future successfully. which is BS.

why I think this is relevant is knowing how people have failed brings relevance to how the construction details in the plans are important.
fallguy1000 wrote: Mon Sep 13, 2021 3:57 pm
Matt Gent wrote: Mon Sep 13, 2021 1:17 pm Sounds like OP wants to build the PH22 like the Morejohn microskiffs. Lots of cool builds going on over there, but the weight and speed are in a different category.

And the 250hp desire is understandable, as so many production 22' bay boats can be powered that way. Frankly if I were going that path, I'd probably draw up (or commission) the design from scratch since you won't be limited by the plywood bend constraints.

Can't comment on the lamination, but I have rebuilt (re-cored) two speed boats, one for +/-80mph and one for 100+. I replaced the existing rotten butcher-block balsa core on the running surfaces with 5/8" Corecell A500. For two reasons - it is much tougher than the PVC foams, and the perforation is set up to vacuum bag it in place for good resin dispersion. I did use Divinycell H80 for bulkheads, stringers, seats - where they don't see the slamming and cyclic loads of the bottom, and are primarily a form for the glass skins. Hopefully you can find a use for the foam you have bought already.
I'll try to avoid extended debate and this is not a critique of your work Matt, but the problem with the a500 core is the interface between the bottom or top deck and the sides. JM will show the OP what to do, but what happens with an a500 core at the hulls edge is massive compression loading. Just think about it like this...instead of the a500 foam, put a neoprene sponge in place of the a500...it does fine until the sides of the boat press down on it. At that point, it is subject to massive crushing loads. So that interface requires special attention. So does the hull to deck interface for same reasons. The deck, in light(er) foam comes crashing down onto the hull sides which do not move and you can actually crush the foams. There are books written on these interfaces. The Skoota does not really need to consider these forces much because the boat is a wave cutter and not really supposed to jump waves, but go fast boats are subject to tremendous loads.

But an a500 bottom to hullside interface may not be sufficient. Again, only for the OP. Generally, a high(er) density core or a no core lamination occurs..but it gets far more complicated to build to avoid busting the boat at high speeds.

fallguy1000
* Bateau Builder - Expert *
* Bateau Builder - Expert *
Posts: 10199
Joined: Tue Jan 12, 2010 12:25 am

Re: Steve's PH22

Post by fallguy1000 »

Oh, boy. All we needed was some Pascoe core hate.

...disregard; mostly
My boat build is here -------->

viewtopic.php?f=12&t=62495

OneWayTraffic
* Bateau Builder *
* Bateau Builder *
Posts: 1663
Joined: Sat Jan 10, 2015 7:13 pm
Location: New Zealand

Re: Steve's PH22

Post by OneWayTraffic »

Everyone has an angle or a bias, as a surveyor (I think he's passed on now) I can understand his. If you are paid to survey a boat, and liable for getting it wrong, cores (especially below the waterline) are a problem. How can you tell whether the workmen paid attention when bonding the core to the outer skin? Did they get it right? Are you willing to risk $$$ on making the wrong call?

As home builders we can work at our own pace, use whatever methods and materials we please, and do our own QA. Different than trying to judge somebody else's work based on non invasive methods.

OneWayTraffic
* Bateau Builder *
* Bateau Builder *
Posts: 1663
Joined: Sat Jan 10, 2015 7:13 pm
Location: New Zealand

Re: Steve's PH22

Post by OneWayTraffic »

fallguy1000 wrote: Mon Sep 13, 2021 8:35 am
So, how does that work in my example for Steve?

Separation of 1/2" core versus 3/4" core is 1.5^2 or 2.25 times only versus my citation of 3.375? (For same skins)

Meaning a 1" core is 4 times stiffer than 1/2" core?

Building this speed demon from foam might require thicker foam and more bulkheads and even more long tees then.

I gotta read that Diab text because this is new to me. And I'm even more curious about the foam plan/layup.

As I understand it yes.

I think the real issue is less the thickness of the core, and more the skin/core interface. At those speeds I'd expect some pretty hefty skins to be specified, which is why part of me wants Steve to build as per standard, and part of me wants to see an extreme build. Either way I will be following this thread.

If there was a pool for guessing the final layup I'd be putting my money on a 3/4" core (at least 100kg/m density) and about 4/3mm of directional glass on the outer skin and inside respectively. I could be way off obviously.

Post Reply

Who is online

Users browsing this forum: No registered users and 10 guests