34' Multi-angle Deadrise: PaPaJ Launched

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kmorin
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Location: Kenai, Alaska

34' Multi-angle Deadrise: PaPaJ Launched

#1

Post by kmorin »

Some years ago I posted, during a conversation here, about the concept of having more than one deadrise angle in the bottom of a planing boat.  I haven't found that post- had some images in it and a brief discussion of why I thought this concept would be worthwhile to build.

A long time friend decided he wanted to build his own 34'er for South Central Alaskan waters and after drawing and discussing his ideas he decided to build on the concept of the various deadrise angles in his hull.  I designed the boat using Delftship Pro over a couple of years following this routine. 

He worked 2 on and 2 off on the Slope (Electrical Supervisor and Project Manager) so he had plenty of evenings (14-15 days a month) to study his plan and make revisions, ask for comparisons and explore minute changes.  I'd take the mark-ups, edit to the current thinking, and print them or email to his Slope office and he'd spend his evenings going over everything and redlining what needed changing or exploration. 

This lead to the final design and 4 years and 6 months ago we started the build in his shop in Kenai, about 1/2 mile from my shop. This fall he launched and while the boat is still having engine bugs, correct props, and engine placement worked out; it is essentially in the water getting some running time.

I don't usually redirect traffic from the Forum to other sites but this series of 52 videos (done solely by the Skipper/Builder/Owner) are located on utube.  The search string "Jahrig Aluminum Boat Build" will return the videos, and I think his channel name is "PaPaJ" which is the name of the boat.

The first thing to mention is that I worked on the boat's design, layout and metal work stages, but the Skipper, Will Jahrig (jer-rig) did 100% of everything else. Will painted her, wired her (he's been an electrical contractor and master electrician for 45 years) plumbed all the systems, did the interior finish and every other task with only an occasional general shop helper to hold the "other end of things."  We did the metal work completely by ourselves with Will cutting and doing some tacking and welding and me doing the remainder of the welding and all the TIG.  We built the hull on a rotisserie after she came out of the female plywood set up jig and that allowed us access to welds and finishing steps not possible if we had to climb in and out of this sized hull.

The bottom of the hull has a central 3' of 27 deg. deadrise. Outboard, in what is generally called the Quarter Buttock line, or just outside of the central V, is hull panel with a deadrise of 15 degrees for a couple of feet, and the outer several feet to the chine is 5 deg. deadrise.  All these changes in deadrise intersect along full length buttock lines (12' deep longitudinals) that run continuously from transom to the bow- where they all curve up to the deck plane; which is flat and runs from the bow stem aft to the main transom. The after bottom chine is 10' wide the topsides 10'-3" just under the helm.

This design is somewhat unique and is not employed by any other plate builder that I could find (researching to see if there were advantages to this shape?) but there is a very significant purpose to the shape.  The bow's entry angle is as sharp or sharper than most planing catamaran hulls while here stern has the very wide 'sponsons' or "30" chine flats" to reduce her roll when at anchor or drifting to fish.

Generally, this class of boat (36' LOA X 10' BOA X 18k lb. wt)  has a single V or deadrise from the bow stem intersection of the chine aft to the transom and both the warped and monohedron shapes are a serious set of trades between running impact and rolling at anchor. 

What we were trying to do was find a shape that could be made out of flat plate (developed shapes no compound curves) that offered sharpened entry and still resisted rolling when not planing.   It appears this hull shape does that but it has only been in small head seas and calm conditions so more experience will be needed before we can pronounce it a complete success.

She has a sweet spot of 1.1 gal/mile (per engine) at about 30 mph at I think 4k rpm(?) and that is where she was intended to cruise.  This conclusion may change a bit as she's still propped at 5400 max rpm's.  However, given the cost of four new props for the Suzuki 350's, or even pitching these down a bit... I think she's enough of a 'hole in the water' right now to stay as she is for the season?  The top end will likely increase quite a bit when the cav plate is confirmed to be high enough in the wake and the pitch of the four props allows full 5.8-6k rpm's.

I suggest that anyone who has built in or is interested in this class? Watch the first 5-6 maybe 10 videos then watch #52 to see her run in low speed tests.

There's not much point in taking up space here with these videos but I will be happy to field questions about the project if there are questions posted?

Cheers,
Kevin Morin


 
 
 
kmorin
dingahling
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Re: 34' Multi-angle Deadrise: PaPaJ Launched

#2

Post by dingahling »

Kevin,
Love the boat and the execution of the design.

Question on the aluminum rub rail - I thought you were a fan of the skip weld in this case, as opposed to fully welded ?
The fully welded looks beautiful, but concerns for excess moisture/corrosion ?

Anyway, thoroughly enjoyed watching the build videos. I'm jealous I don't live closer to your brain trust and talents.

Thanks.
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Re: 34' Multi-angle Deadrise: PaPaJ Launched

#3

Post by welder »

That Bow defiantly stays down at cruse, I like the spacing between the motors for handling purposes and she really looks comfortable.
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kmorin
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Location: Kenai, Alaska

Re: 34' Multi-angle Deadrise: PaPaJ Launched

#4

Post by kmorin »

dingahling,

I'm not a fan of fully welding rub rails, but this was not my boat and I was 'crew' in the building. Yeah I designed her but I don’t own her or make final decisions for the Skipper.
 "The Skipper is Always Right" phrase is the general retail trade axiom from the "Customer....Right! " As the designer of the hull form; my real influence stopped at the deck where the Skipper's ideas carried us (sometimes with me kicking and screaming) upward. (I became more influential at the cabin brow again but only briefly!!)

The rub rails (even the lower 'dock rail') are made from 'hull stiffener' extrusion from Ak Copper & Brass. To look up this ( 230980 PN) extrusion you'll find the two legs of the 'round corner channel' are 3' side to side at their lower ends. The top or 'web' is only 2' above the legs' ends and the entire section is about 3/16" thick or 0.188". 

On this boat we only used the full depth of the extrusion on the 'dock rub rail' the lowest near the water line. [ https://www.alaskancopper.com/Aluminum_rod_bar_shapes from this page locate the Hull Stiffener and you'll display a 'PDF' of the section]  This rail was formed by slitting the Hull Stiffener (HS) along its back center-line and using each side as an 'sloped angle'. The sides were separated in a welding jig and a series of flat bars held them equidistant apart until the assemble was on the hull- tacked and welded out. I later built a forward end of each dock rub rail in what I thought was a complimentary shape to the hull's location and overall look of this rail. This set of rails holds a series of long blocks of plastic that have been ripped to width then grooved to slide into the dock rub rail frame. 

Next upward on the topsides, including a very thin version at the shear, are a series of HS extrusions that have had the legs cut off so they're not fully 2" tall. THEN... and this is super critical to the welds that followed; the ends of the legs were mitered/chamfered at 45 deg with a router. Once applied to a flat surface there remains a void or weld allowance under the leg- the leg's outer surface is raised above the flat surface and the inner edge of the leg is knife edge touching the flat (topsides) surface on which this will weld.
 Left alone, I’d have skip welded these extrusions but the Skipper wanted a better paint joint and so they were welded continuously top and bottom.

Now an aside.

I TIG weld using the OTC Daihen 300 A, water cooled TIG Gun. This torch feeds the wire into the puddle and is adjustable for amperage (or peak pulse) and wire feed speed. I welded the several hundred feet of the lower rub rail extrusions’ legs to the side of the hull using this torch. I am not that good with a two hand dip method but even those guys who’re very good- might have found this overhead weld challenging?
 

The result was some small ‘side wrinkles’ that were the direct result of the combination of decisions by the Skipper. I suggested we ‘super stress’ the topsides in both Section and Plan but those requests weren’t accepted so the topsides don’t hold enough sheet tension to overcome the weld contractions - even when the weld is fully inside a bevel and the topsides. While I was able to reduce to a very small amount most of my weld contraction- I was working as crew not the builder.

She’s not utterly homely, or even ‘hungry sided’ like a starving horse but this hull might have been cleaner if we’d follow some ‘learned lessons’ more closely and changed the topsides shapes to more warp, camber and tension in the sheets- or adjusted the welding pattern to skip instead of continuous.
 

The extrusions are all drained at their stern caps and at the low point of their curves so I don’t think we’ll see much standing water? Also, the topsides were both buffed of all mill scale and etched before paint so I think we’re pretty good for corrosion cells? most parts/panels/plates that were less than 50” wide were cleaned in a drum sander with a hook and loop ScotchBrite (3M tm) surface abrading belt and that sanding/buffing/cleaning was often followed along the edges with a narrow buffing just prior to welding.

More than casual care was given to cleaning the mill scale off, and while on the rotisserie the inside of the hull was etched, even though most of the parts were buffed in the drum sander prior to tack up or weld out.
 Hope this helps with the series of decisions around the welding of this hull? 

Cheers,
Kevin Morin
Kenai, AK
 
 
 
 
kmorin
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