Aluminium boat Panama

Steel and aluminum boatbuilding. See: "Boatbuilding Methods", in left-hand column of the Home page, for information about alloys.

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Kevin Morin
Posts: 697
Joined: Thu Jan 24, 2008 11:36 am
Location: Kenai, Alaska

Re: Aluminium boat Panama

Postby Kevin Morin » Sat May 12, 2018 2:54 pm

niko,
If this is a first build in metal (in any material??) then please allow me to suggest you'd be well served making a model? Not sure what plywood products you can acquire in your location? BUT... I will say that I have coached more than a few new metal builders- many of whom told me to pound sand at the suggestion of a "DELAY" in their immediate building in metal!

On the other hand- the boats that resulted: I separate into two groups. First are those who told me to pound sand- and they'd be fine just going forward with metal and learn as they go!! and most of the incomplete or purely junk boats are all confined to this first group of people who needed help, asked for help, and ignored the help they were offered.

Second are those who built a scale model of their boats in very thin plywood. (one used thin sheet aluminum and used a hot glue gun to 'weld'!!) Others used poster board (I've done most of my hull models in poster board and hot glue- but in the old days I used wire strips at the seams). This group has the highest success rate of completing a metal boat and having something they might resell - an not be ashamed of the number of errors!!

So, while you're welcome to say that I'm being overly cautious about building a first boat in welded metal instead of using a model to 'fully understand' the plans? I will suggest you consider this exercise in sheet boat building so you get some ideas of the issues before you?

the ply or paper thickness is critical to this potential exercise. If you make a model in too small a scale- finding proportionally thin sheet will be difficult: UNLESS you use sheet relatively close in proportion to the models' LOA, in scale, you will not learn to form the boat - deal with fairing issues or teach yourself useful lessons.

Simply put, if you don't acquire, construct, provide for a reasonably proportioned 'skin' or veneer/plywood product, or a sufficiently useful paper product? then the modeling step is of no use to your learning. ON the other hand: if you're not able to provide yourself a proportional modeling media? I doubt you (anyone reading) has the resourcefulness to build a welded metal boat?

We've not met, I'm not being rude or casting aspersions, I'm simply reporting on my experience as regards online tutorials of welded aluminum boat builders. So, please don't take offense at my very accurate remarks about the skills required to build in welded aluminum?

niko, I'll take a shot at some of the unanswered questions in other replies?

cheers
Kevin Morin
Kevin Morin

Kevin Morin
Posts: 697
Joined: Thu Jan 24, 2008 11:36 am
Location: Kenai, Alaska

Re: Aluminium boat Panama

Postby Kevin Morin » Sat May 12, 2018 3:24 pm

niko,
to begin to reply about scantlings I need to make some general notes about the Glen-L catalog and 'mail order' (now days online) boat plans.

Most important is that anyone who's buying a build-it-yourself plans package is usually not a professional boat builder- or even a full time builder- regardless of material. That statement is applicable to all three materials systems: wood and plywood, glass reinforced plastic resin (fiberglass), and metal boats- all have professional and personal use builders.

If you perform any trade full time your proficiency becomes much greater than someone who does a full time job in one sphere of work but comes home and on their week ends- builds a boat in their "spare time". The first example is someone who's engaged all the time in the skilled trades- but the second is someone who's engaged 40 hours a week (or more) in other endeavors- and they only get a chance to exercise their skills after hours or on the weekends.

Back to the main buyer of Glen-L plans. The typical buyer is someone who may not have the full time trade skills of a finished carpenter, a certified welder, or someone who works with glass cloth and resins during their regular weeks' work. That means the plans need to be simplified compared to those that are sent to a full time boat builder- these necessary simplifications take all sorts of forms. Put another way: the designer has to provide a set of plans that the less skilled worker can follow to end up with a nice clean boat.

I'll just address metal plans from here on in this post. In a metal plan- Glen & Ken have no control over your welding ability, skills, resources or experience. So their plans packages try to provide for the lowest possible skill set - which allows more skilled tradesmen to ignore or modify given design elements without compromise IF..... (huge word meaning in two letters) ..... IF the builder has sufficient knowledge to recognize the potential to make a change- and not compromise the boats' integrity.

This statement implies that anyone who has to ask if they can make a modification to the scantlings, design, or building plans: SHOULD NOT DO SO! Kind of a "Catch22" in plans reading. "IF you have to ask if you can make changes, you're not qualified to make changes: BUT any changes you make should only be made by those qualified to understand the effects of those changes- all of whom won't ask"

That is my preface to your question about the VKB (vertical Keel Bar) even as it extends up the forefoot to the bow stem (the intersection of the two topsides hull plates/sheets).

The plans call for 3/8" and perhaps you have a paper pattern from the Profile View (?) that you could lay on a single piece of material and centerpunch and batten a set or curves to cut into a stem (VKB above the chine)?

If I understand your question (no pictures or links??) you're asking if #1 you can piece together a set of 3/8" narrow planks/bars with weld joints between the smaller pieces- and then create the needed longer (possibly curved) shape to cut the VKB bow stem?

IF, that is your question? Yes you can do that method of construction. However it is not quite that simple, the blank cutting, assembly, tack up and welding is a bit of a procedure- but once welded it can be 'hammered straight' and from that flat piece the forefoot and bow stem can be cut- disregarding the weld seams.

my opinion of boat building is that no 3003 alloy should ever be used for any structural element of any kind- anywhere. That alloy is not a "marine alloy" so the mechanical properties and the corrosion resistance are not the same or close enough to similar to 50 or 60 series alloys to consider including that material in your build.

As to substituting 1/4" 5052 for 3/8" 3003 - that is a good idea!! however depending on the outline patterns of the hull? you may need to add a 'whisker' to each of the topsides for the loss of that bow stem thickness.

extrusions will work fine for longs- and long strips of 5052 sheet that was sheared from sheet material with curl, twist and otherwise distort in the shearing process- so extrusions are a good substitute. The all 50 series alloys would be preferable but unless you can find 50 series extrusions (rare and costly by comparison)- 6061 bar extrusions will work fine.

AS to hull longs- they may need to be lofted and sawn from sheet as diagonals in the forward 25% of the bottom of the hull- bending extrusions is usually quite and exercise for most first time builder.

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin

Kevin Morin
Posts: 697
Joined: Thu Jan 24, 2008 11:36 am
Location: Kenai, Alaska

Re: Aluminium boat Panama

Postby Kevin Morin » Sat May 12, 2018 6:15 pm

niko,
This post is about my limited understanding of the Delta Pad hull feature. AS far as I know this idea (#1) is to reduce the depth of an outboard engine's anti-ventilation plate in the water? In my outboard engine installation experience- an engine's "cav-plate" as the lowest horizontal plate just above the propeller's tips is supposed to be a 'given' distance under the RuNNing water line.

That is a bit of a problem as almost any wake from the bottom of a planing hull will have some rise the farther is is aft the transom release point. Speed, shape of the bottom, load and beam of the boat all seem to contribute to this 'wake wave' swelling upwards just behind the boat. In fact- this variable is so widespread- there is an entire product designed to allow the boat operator to raise and lower the engine (vertically not trim-tilt) just to compensate for the different conditions the boat is experiencing; the Hydraulic Jack Plate. https://www.wholesalemarine.com/boating ... lates.html (For example)

If a hull has a 15 degree or greater deadrise/V bottom angle (per side in Body Section View) then the hull is deeper at the centerline of the keel by several inches than it would be if the deadrise were flattened just forward of the engine's a'vent plate. At a 15 degree V at the transom; a 12" wide D'Pad would cut off 1-5/8" (41mm) of engine depth (rough) and at 20 deg. the depth savings is about 2-3/16" (55mm).

This is solely based on the removal (as in your pic #2) at the transom, of the bottom 12" width of the V, as designed. The engine's a'vent plate can be these distances farther UP leaving the engine cowling farther of the water! while not much- it is some less immersion of the engine while at rest. (#1)

Next is the 'rise of the wake', aft the hull- (#2) the rise along the centerline of a V may be different from the rise of the wake with the D'Pad - and that is contended by some designers- I'm not positive- but it is offered as fact in some circles of marine design? (You'd have to explore someone's explanation besides mine!) But the point is; the a'vent plate could be even higher up! than the depth savings shown above- say and additional 2" or so?

the D'Pad offers one transom design that benefits a short shaft engine quite a bit; mounting as much as 3-5" higher in relation ship to the at rest waterline. (#1 & #2)

Concerning to speed: it is claimed the D'Pad will help increase top end- again (!!) I don't know that to be a hard fact? I'd only be convinced by two identical boats, wt/load/ engines props and all - shown identical and then run side by side? Such a test may have been done by D'Pad boat makers? I've read about the advantages but cannot report to you from my experience in building. I've equipped a couple of skiffs this way- cutting off a V and installing a long tapering flat over the former V sections BUTTTTttttttt....... I didn't have any comparison to the previous shape's performance as this was an engine and bottom change/modification.

finally, (#3) the reason I brought up the D'Pad for your application was to keep the hull upright when it beaches. In the case of a relatively flat beach, with a low tide exchange, and guests climbing over the gunwales to get to the beach... I thought keeping the hull upright was desirable?

So I suggested you modify the existing plans to include a D'Pad- get the engine up farther out of the water (could buy a 30" shaft now days?) raise it further due to wake rise (can't confirm this is a gain for D'Pad) and last- to give some flat spot on the bottom to stand the hull on when you're beached and loading or unloading?

The geometry of this could be done by simple drawing a pair of lines on the inverted hull during the build- from a point - say 6-10' forward of the transom and bottom intersection, on the keel; to the two symmetrical points along the transom to bottom intersection line- and that is the cut out.

If there are ribs in the way? they'd have to be cut off (upward into the hull) and a long triangle or plate would fill this new shape- the Delta Pad. Since this small cut away will 'run up' that is the monohedron or uniform V prism shape will have a plate running UPwarD - aft- this reduction in the hull's planing support surface will result in a small 'squat' or lowering of the stern when running. This is hard to estimate since the cutout is such a small area- but the aft most 6" of the D'Pad can be hooked (slightly rolled downward) or trim tabs- dynamic or fixed can be installed to help compensate for any bow (up) pitch resulting from this potential modification.

Hope this helps you consider the D'Pad modification to your hull? I don't have the lines or plans so I can't really say too much about what the effect will be on this particular hull- but I've given what I think is a general idea of the performance changes?

Please let me know if I can help with any other design element reviews? I'm not sure if the hull leaning over on the keel-to-chine side of the V of the bottom; is acceptable? I visualize that getting guests in and out would be less 'gymnastic' if the boat were on an 'even keel'?

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin

niko
Posts: 13
Joined: Fri Apr 20, 2018 7:20 pm

Re: Aluminium boat Panama

Postby niko » Sun May 13, 2018 8:18 pm

Your suggestions, tips and explanations are great and none of them can insult me. But truth hurts :wink: and the idea of the model really hit me hard.
I will definitely do that first now because it can answer me many questions I still carry around. What scale would you use? About 1:5?

Yes sometimes asking how to change something means it shouldn't be done by the one who asks. I got that one :wink: maybe after this boat ir even after the model I will know more. Yes it is a first time build and I am trying to read as much as I can about the building process and studying S. Pollards book and your posts.

Yes you got my question right on the stem. so best using 3/8 10 or 8in 6061 flat bar and weld them in the right shape to cut out the rounded bow stem. Worse using 1/4 5052 plate and cut it out and worst and in no case using 3003 for the stem.

The Deltapad stuff is very interesting and I am looking for information everywhere. Yes it would help me with the Motorlength and to stabalize on the beach.
I was thinking that it would be bad to have the keelline moving up towards the transom but you gave me a good explanation that I could work with. Maybe the model will help too.

To prepare the longs in the bow I already read a few of your posts and will also use the model to try things out.

Thank you for all the patience of yours!
Best wishes from Panama

Kevin Morin
Posts: 697
Joined: Thu Jan 24, 2008 11:36 am
Location: Kenai, Alaska

Re: Aluminium boat Panama

Postby Kevin Morin » Mon May 14, 2018 2:53 pm

niko, 1:5 scale is a good place to begin- this allows parts to be thick enough to teach lofting/layout and forms or frames are somewhat realistic when stood up inverted to begin the plate take-offs.

I don't think I wrote very clearly on the bow stem material/scantling. 1/4" material, regardless if it is formed from flat bars then layed out for curves/profile shapes- or cut from sheet- it will be fine. You do not need the 3/8" bar but there are implications to changing this material- I was trying to encourage you to consider the implications of the changes- not to discourage the substitution of 1/4" for 3/8".

I suspect the material is specified to give a bigger target to bring the topsides' forward edges against and weld effectively? Don't know that but I've build plenty in the 20'-25' range and can state that you don't NEED this size bar. I think Glen or Ken was "designing defensively" - where they can't begin to predict anyone's welding skills (or fitting skills for that matter?) and specified a big bar to get a wider target to back up the stem welds?

However, until we share the weld joint sections' images or clearly define intersection of the three pieces of metal at the bow- I can't really confirm this substitution. So you'll have to look at your plans and learn (?): Does the bow intersection (in the Plan View) show the sheets on the sides of the bow stem? ( is the Rabbit line aft the leading edge of the bow stem bar?) Does it show the sheets' leading edges fair "knife edge" to "knife edge" to the bow stem's leading cut edges? OR some other joint (in plan view section)???

This will influence your final joint design and materials planning.

niko, I didn't finish my metal boat building thread- the one with methods of build- and the next chapter/post would lead to fitting the bow longs- as either diagonals cut from plates, OR bending some other material for these longs. NOT all bow or forefoot areas require this super tight curvature but many of them do. So the Methods Thread will need to introduce the problem, and then show methods of lofting solutions, cutting and then fitting them to the frames and bow stem if there is a VKB in the plans?

You're welcome to any information my years of making mistakes has allowed me to retain! Metal boat building can be very recreational and result in good quality boats that serve for entire lifetimes. But there are plenty of mistakes to be made - so my goal is to help those who post questions avoid my list of mistakes, hopefully reducing their learning time an improving their initial build too?

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin


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