Building an offshore aluminum duck boat. What material?

Get help and share Ideas
Longtailassassin
Posts: 1
Joined: Sun Jan 27, 2019 1:13 pm

Building an offshore aluminum duck boat. What material?

#1

Post by Longtailassassin » Sun Jan 27, 2019 1:36 pm

Hi all. This site was recommended to me from a friend at the Hull Truth.

I am looking at building a 23-24' aluminum Duck Boat. It will be used to transport 2 layout boats. In essence this boat will be a tender boat. Sometimes we get stuck in rough seas, shallow seas, or frozen launches where we need to break minimal ice to get in or out.

Proposed hull specs:
1/4" bottom. 10-15degree hull with a higher rised V or mod V front. It needs to bust through waves but also not draft a lot of water. 80" or so wide bottom

1/8" sidewalls 36" high

1/4" transom

Longitudinal stringers with a 10" cross bulkhead structure system

1/8" aluminum floor

2' pods in the rear with an outboard motor bracket (200hp 4 stroke outboard)

I need it to be 100% aluminium as I do not want to worry about rot. My question is what kind of aluminum would you experienced builders use? 5086, 6061, yada, yada.
Also, what type of mig/spool gun wire would you use? The bulkheads would be bent on a break.

Thank you in advance.

kmorin
Donator 08, 09, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19
Posts: 1436
Joined: Mon Aug 18, 2008 1:37 am
Location: Kenai, Alaska

Re: Building an offshore aluminum duck boat. What material?

#2

Post by kmorin » Sun Jan 27, 2019 8:55 pm

Longtailassassin wrote:
Sun Jan 27, 2019 1:36 pm
I need it to be 100% aluminium
I think you may have answered your own question?

I prefer 5086 as that is most cost effective and 'stiffest' readily available alloy in the PNW. Other areas may have 5083 which is very nearly the same material.

Bending bulkheads? do you mean flanging the panels? - not really good practice in welded boats since the flange to hull panel forms an area that creates a thin film of retained water due to capillary action and also leaves the bottom (chine to keel) & topsides (chine to sheer) as straight lines- these imply 'flat' panels and they are subject to weld contraction distortion much (MUCH) more so than convex panels where a bulkhead intersects a bottom or topsides panel in a T fillet joint.

Many designers use a cambered Body Plan (section view) for the chine to keel and chine to sheer lines. Not all, but flanged bulkheads are not common practice in today's welded aluminum boats.

10" OC "cross bulkheads" or do you refer to 10" OC transverse frames? (usually) Frames would be stitched to the hull panels, only bulkheads would be welded solid creating a "bulkhead".

you can use 0.0125"-1/8" for the topsides but at 3' tall and 24' long they'll need an extra set of longs (stiffening from chine to sheer along the length of the sheet) and closely centered x-verse. It is very common in this size range to move up to 5/32"-0.0160" and reduce the framing effort while ending up with the "same" stiffness in less work; spending $ in materials over labor and welding distortion potential. it is not uncommon for a 23-26'er to have 3/16" sides if the bottom is 1/4".

in this size class, adding trim tabs to the engines' trim/tilt function more often allow a bow pitch dynamic providing the pilot more freedom to use the power to obtain trim and pitch by the bow. Using 'pods' or ama's along side the engine(s) reduce the bow pitch my moving the engine thrust moment forward and allowing the two 'pods' (hull plane extensions) to have bow down pitch moment AFT the thrust.

In this condition, unless you'd built several of these hulls (so you had performance reports) the result will be a serious reduction bow pitch control. That can (might not?) result in a long increase in time to get on step. If the bow can't trim up (due to hull extensions aft the plane of thrust) then 'climbing' the wake or Planing can take much longer.

Choosing welding equipment can be a challenge if you have no welding experience. Unless I could understand how long you've welded with which types of equipment- MIG (push-pull? spool gun?) TIG? it is nearly impossible to recommend what was a "safe" path for your work.

If you are learning to weld? I'd say the project was pretty ambitious!! Good luck, with your boat, sounds like an interesting design. Do you have images of a boat already doing this work?

Cheers,
Kevin Morin
Kenai, AK
kmorin

MacCTD
Posts: 517
Joined: Tue Jul 22, 2008 2:53 pm
Location: MA

Re: Building an offshore aluminum duck boat. What material?

#3

Post by MacCTD » Mon Jan 28, 2019 12:02 pm

These guys build boats that look similar to what you are talking about building https://duckwaterboats.com/
'05 Pacific 1925
Honda 90hp

alumioforte
Posts: 95
Joined: Sun Nov 27, 2016 8:08 pm

Re: Building an offshore aluminum duck boat. What material?

#4

Post by alumioforte » Wed Jan 30, 2019 10:52 pm

Is this your first build? For the money and time, its DEFINITELY more sensible to have an experienced builder do it. The only reason to build yourself would be just to say you built it yourself.

User avatar
gandrfab
Posts: 428
Joined: Fri Mar 28, 2008 12:33 pm
Location: Edgewater Fl

Re: Building an offshore aluminum duck boat. What material?

#5

Post by gandrfab » Thu Jan 31, 2019 5:24 am

Have you seen the mark up builders put on boats these days?
If one can do it one can save a few bucks.

kmorin
Donator 08, 09, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19
Posts: 1436
Joined: Mon Aug 18, 2008 1:37 am
Location: Kenai, Alaska

Re: Building an offshore aluminum duck boat. What material?

#6

Post by kmorin » Thu Jan 31, 2019 12:29 pm

G&R, welded boats aren't cheap and anyone WILL end up with a serious material investment anyway you go... But a new builder is sort of risking a lot of material money as they learn on that first project. So I think
alumioforte wrote:
Wed Jan 30, 2019 10:52 pm
For the money and time, its DEFINITELY more sensible to have an experienced builder do it.
is reliable advice- I'd say a few skiffs in the utility, flat bottom class are a wiser path of learning than jumping in on a V bottom specialty design project? Just my take; that first half dozen or so skiffs are a real education for most of us!

EVEN If; a kit or cut file plan set were available (?) to reduce learning about layout and cutting techniques.... I'd still say a single one-off 24'er would be a real challenge for a first time builder. So, "for the time and money"....

Cheers,
Kevin Morin
Kenai, AK
kmorin

User avatar
gandrfab
Posts: 428
Joined: Fri Mar 28, 2008 12:33 pm
Location: Edgewater Fl

Re: Building an offshore aluminum duck boat. What material?

#7

Post by gandrfab » Thu Jan 31, 2019 1:12 pm

I understand.
And I obviously haven't jumped in to the boat building game.

alumioforte
Posts: 95
Joined: Sun Nov 27, 2016 8:08 pm

Re: Building an offshore aluminum duck boat. What material?

#8

Post by alumioforte » Thu Jan 31, 2019 7:19 pm

Definitely at least do a Specmar or Metal Boat Kits kit. If you're in Seattle, I'd be happy to help mentor where we can. An experienced welder with $12,000 welding machine will cost you only $65 an hour. Where you can have a better chance at saving big bucks is if you do the rigging yourself- its harder to mess up installing electronics, windows, carpet, trim, etc than it is to mess up forming and welding of aluminum. :thumbsup:

Post Reply Previous topicNext topic