34' Multi-angle Deadrise; PaPaJ Launched

[Kevin Morin]

WeldingWeb isn't very crowded with welded boat projects so I thought I'd share one. The pictures, videos and voice commentary by the Skipper/Owner; Will Jahrig are all on utube and mentioned below.

I have been interested in designing a welded aluminum boat that could solve some of the problems with these boats that I'd experienced over time. This post introduces the first large scale test of those ideas. The primary concept is to design and build with more than on V angle (deadrise) in the bottom of the hull. This might offer a sharper, smoother water cutting and entry while at the same time allow a nice wide stern with nearly flat outer chines aft. The boat would be intended to run faster into a chop or 4' sea, while rolling less in beam sea while at anchor or fishing.

A long time friend, Will Jahrig, 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 (software) 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 a 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 (video #1 @ 6:49) while her 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

[rexcormack]

Some photos would be good.

Thanks.

[shallowwatersoul]

So I ran across this papaj build on YouTube and I was immediately hooked. I’ve watched all the videos he has made and I just knew it would have been documented on here. Very very impressive build. In some of the video clips I saw the tig “gun” spool feeder looking machine. Can you give some insight on that machine and how it works? I’ve never seen one like it

[_Dom]

Thanks for posting this Kevin, I always appreciate your willingness to share expertise.