NEWB- First build Jimbo questions before starting?

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2fish
Posts: 4
Joined: Fri Aug 24, 2018 5:15 am

NEWB- First build Jimbo questions before starting?

Post by 2fish » Fri Aug 24, 2018 6:32 am

Here it is. I live in S. NJ and want to build a custom pocket fisherman for back bays. Garvey style boats used to be very common place in this area (I think the original design was from NJ) and I feel like the relatively simply design will work well for my needs. I want to be able to carry 600-700lbs of people in gear in the finished boat and still be able to hit 20-25knot cruise, be able to clam, crab, and fish. Back bays can get a little sporty at times and I may want to go out front on the occasional calm days. I am a machinist with welding experience, have a spool gun for my welder and love to create.
Am I looking at the right design to start?
Any challenges that I should consider before diving in?
What is the real cost of building one of these less engine and trailer?
Pics, pics,pics, Please

Kevin Morin
Posts: 699
Joined: Thu Jan 24, 2008 11:36 am
Location: Kenai, Alaska

Re: NEWB- First build Jimbo questions before starting?

Post by Kevin Morin » Fri Aug 24, 2018 10:35 am

2fish,
a welded aluminum, garvey hull form will do all the things you've listed as priorities for your project. A 60"/5' chine to chine (beam on the water) will haul the loads you're describing but a 72"/6' wide chine will do so in less depth or draught of hull. (few inches difference)

Using a 5' or 6' wide bottom sheet makes sense in planning because they are both routinely milled/rolled/stocked sheet sizes at metal vendors, but of course I'm not familiar with your coast's suppliers' stocks- just stating that these are normally available on this coast.

The hull shape has little curvature- the most challenging aspect of metal boat building for new or first time builders it seems? so it will be less difficult to layout/cut/form up and tack the hull because it has a reasonably uniform "run" aft the Master Station (widest point about 1/4 to 1/3 LOA- aft the bow)

The bow is usually pretty truncated- or cut off flat in a transom like plate so the work of pulling sheets around in a higher level of curvature and tacking is reduced. The hull's bottom is usually flat or only slightly V'd or cambered (cupped downward), again simplifying the layout and design elements of framing and sheeting this hull form.

All this adds up to a simplified hull, when compared to a deeper V, fully formed bow with a sharper forefoot most often found in off-shore designs like the Chinook or even the Dory series in Glen-L's catalog.

AS to pictures, I think you'll have to use the Search function and the Boatbuilders' reporting sections from the home page? Both these resources should help you find others' builds- but I'm not sure the Jimbo has been done in metal- just assuming that any that exist will be listed in those sections?

I haven't built in that form, but have done numerous skiffs in the 16' to 26' range of welded aluminum. I'll go look at the Jimbo to see if there's any further remarks that I may note to help.

As to performance, garveys are usually more full, or wider in the forward 1/3 of the hull than a sharper bowed cousin. This means they will tend to pound a bit in a higher sea or swell by the bow- if traveling at planing speeds. BUt.... that also means they will lift a very heavy load over those same seas- at a slower travel pace- when compared to the narrower bow sections of a sharp or sides-to-the-bow-stem design. I think that is why they were evolved- to get a higher load capacity for the 'same' LOA- clip the bow and make the forward chine and sheer wider in proportion to the length= higher displacement forward= greater load carrying for any given waterline.

Hope these notes help with your planning?

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin

Kevin Morin
Posts: 699
Joined: Thu Jan 24, 2008 11:36 am
Location: Kenai, Alaska

Re: NEWB- First build Jimbo questions before starting?

Post by Kevin Morin » Fri Aug 24, 2018 11:10 am

2Fish, after looking at the lines plans shown on the plans pages for the Jimbo, I'll remark about one design aspect you may want to consider?

IN the Body Section Plan page- the sections of the chine beam taper aft. The chine curves in toward the keel in Plan View as shown by the narrowing chine point in the Body Plan. This means the planing surface is tapered aft- by quite a bit? Meaning; several percentage of the planing surface are reduced from the Master Station (widest point about Station 5-6) as the Sections are taken in after half of the hull (left side of the Body Plan image).

Tapering the planing surface is a very touchy thing to design. The top speed and turning attributes are very much effected/affected/determined partly by this Plan View curve's proportions. At slower speeds a highly tapering chine doesn't have as much impact but at higher speeds the influence of this curvature in relation to the overall size is very important to plan.

In the lines shown, the boat will turn VERY agilely, "on a dime" and would be very useful for getting the bow to a trap or pot buoy in a breeze or swell. That tapered chine allows the boat to heel rapidly in turns- allowing a much faster rate of turning ; all that allows the commercial fisherman to put his bow man "on the gear" to catch the buoy with less tries - using an outboard with a tiller especially.

What the tapered chine does at the higher speeds is two performance impacts- one it take more HP to plane the hull due to the slight 'squat' or bow up pitch when adding power to 'get on step' or transition from displacement to planning attitudes while running. The amount of taper to this existing chine- is higher than other planing hulls so... it will have a slightly longer period (seconds) of bow up pitch to get over the bow wave and plane- for a given HP. This can be overcome with more HP (higher in the suggested range) OR with a anti-cavitation plate lifting fin/plane.

Neither is much in convenience. The last impact is steering at high speeds with light loading. This hull, as drawn will have a touchy helm at high speeds- >35knots. The boat is very light, the planing surface has lots of taper and those combine will leave the helm more sensitive than a similar size boat with more parrallel chines. But that latter design is not NEARly as agile in regard positioning this size skiff onto floats when pot or trap fishing.

If I were considering this design I'd adjust the chine on Frames 6(widest point?? confirm) aft to the transom so the chine at each Station was less tapered than shown. This can be done on the plans by simply drawing a new chine line in PLan View. split the difference between a dead straight line in Plan view (master station chine offset @ #6 the same as transom) and the currently shown taper.

That will result in the same V bottom or deadrise at the transom but... less taper for the planing surface and less sensitivity at the helm at top end. Full speed turns will become slightly wider radius- so instead of making a 50' radius turn (for example only) the added chine beam aft, will result in a 70 or 80' radius turn. That example is for comparison not some prediction of Actual turning radius.

Hope this OPINION... (ONLY) about one single aspect of this nice little Garvey doesn't cause confusion or in anyway act to dissuade you from building the Jimbo in aluminum. The change to the plans (shown) will not impact the boat in any drastic way. It will result in an inch or so different at rest waterline or pitch of the bow, a slight change in planing (coming out of the hole) and a little less slew at the helm while running at full RPM's.

I notice the scantlings table given for metal- (mostly 3/16"!!) so... they're very strong for a 16'-17' skiff! She will be a "tank" and much easier to weld than if she were 0.100" or even uniformly 1/8"- 0.125" thick material! I would be comfortable building of 5052 using 5356 wire because the design's scantlings are so generous for this size/LOA; 5086 and the other higher tensile materials aren't required. All the extrusions will probably only be available in 6061-T6 so that ends up being all a builder can readily buy.

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin

Yofish
Posts: 9
Joined: Wed Jul 04, 2018 9:40 pm

Re: NEWB- First build Jimbo questions before starting?

Post by Yofish » Sat Aug 25, 2018 10:27 pm

Always wanted to build a garvey because? Other than a dead-flat river boat or a codfish dory (heh, heh, Kevin I'll add an old Cook Inlet dory?) there isn't anything build wise that taxes in terms of materials and the required effort. I CANNOT give the details of every thing that kevin does in terms of 'this and that' but I can say that one would be hard to find an easier skiff to build as a first off endeavour using plywood or AL. For grins, I did a 'plan' after diner for a 20 footer x 5' bottom (good choice, Kevin) that I'm sure based on previous experience would drive just ducks with 50HP, perhaps less depending on how bold the builder was with hull thickness and scantlings - now THAT is a devil of details - if there ever was one!

Mind you, this is hardly a real plan but the shape is so simple that making it developable is rather easy.
Paul_Garvey.jpg

2fish
Posts: 4
Joined: Fri Aug 24, 2018 5:15 am

Re: NEWB- First build Jimbo questions before starting?

Post by 2fish » Sun Aug 26, 2018 6:21 pm

Thank you very much for the detailed replies. This is a lot of information to take in. I dont think that I have actually given this deep of thought to a boat design. I have been rec fishing and running boats for most of my life and I have 25 years experience in machining (own a pretty good size shop). I am ordering the plans tomorrow. After I have them in hand I need to reread this and try and understand. If I'm understanding correctly the widest point of this design is closer to bow and then tapers to stern. This causes a quicker handling but slower to plain boat. If I'm understanding correctly the suggestion is to straighten (increase width aft) to make a quicker planning and slightly less maneuverable boat. Seeing as I am a rod and reel rec fisherman it's likely a good idea. The more room I have on deck the better.
At this time my biggest concerns have been balancing the boat when complete. I want the console closer to bow and plan on adding a Tee top to keep out of the sun.
Haven't given alloy selection much thought at this point. I run 6061, 2011, 7075 as machining alloys. Most of the structural extensions I see are 6063 or 6061. What is my best bet for sheet in the case?

Yofish
Posts: 9
Joined: Wed Jul 04, 2018 9:40 pm

Re: NEWB- First build Jimbo questions before starting?

Post by Yofish » Sun Aug 26, 2018 8:40 pm

2fish, I'd make the bottom out of 5086 (for stiffness) and the sides from 5052 (for economy) unless the design in terms of length and width makes it easier and more economical to get 'X' size sheets. One could do the whole of it from 5052 but the scantlings may needs be adjusted as 5052 is a LOT wimpier than 5086. Also, a choice has to be made as to bottom thickness which has to do with duty. I'm not familiar with the design you have chosen and I can't find "custom pocket fisherman" here.

Kevin Morin
Posts: 699
Joined: Thu Jan 24, 2008 11:36 am
Location: Kenai, Alaska

Re: NEWB- First build Jimbo questions before starting?

Post by Kevin Morin » Sun Sep 02, 2018 3:40 pm

Yofish, quick note about the Site's plans catalog.

You can put up another page/tab/screen with the Glen-L Plan's catalog links and go to the welded aluminum section (lower on the page) and find the Jimbo as a just under 17' garvey on the plans package links page that pops up. Then click this link and explore, where: you can find the BOM/scantlings and discover the bottom is specified as 3/16" (!) which even in 5052 for a 16-17' skiff is probably more than enough to provide a firm foundation on which to base this little boat?

So, a 16'-17'er with a 3/16" bottom scantling could be built without moving to the much stiffer (and more expensive) 5086- that I'd naturally specify for every powerboat I build. But then I'd spec this boat's bottom in either 0.160" (5/32") or even 0.125" (1/8") just to keep all up wt down. However, the Glen-L catalog's welded boats are often designed for new or inexperienced builders so both Glen and Ken seemed to 'error-upward' in scantlings?

I think I'd even build this little girl in 0.100" and run inside and outside longs -with decks as the only xverse and she'd be fine. But then welding that thin for anyone not experienced using small wire on thin material OR, equipped as I am with motorized cold wire feed TIG: could be an exercise in frustration. So while experienced builders may be able to weld thinner sheet; it is a potential project killer for the newer welders; so we see a 3/16" plate spec to accommodate the skills implied by the newer builder.

Hope this helps shed some light on the Jimbo's scantlings (& where to find them) and why I remarked about the boat being a "tank" when she's built to spec. Also, hope to have clarified that what Yofish and I might consider "doable" - will likely require a new builder to finish a few skiffs to understand.

2fish, adding that much wt (console and T top) to the skiff may be something you'd best consider with design that features a wider chine? Yes, your are correct the Master Section is about 1/2 the Length Overall (LOA) but moving a load up to or onto the point may 'unbalance' the design? I can't estimate your T-top wt? so I have no idea what it adds to the all up displacement.

My remarks about the chine may not be very meaningful if you don't "see" the lines plan and understand the implications that the chine tapers aft (from the widest point of the hull about 1/2 LOA) and that taper has benefits -but some detriments depending on how the boat is used/crewed/loaded. NOTE: typically the catalog does not show the Plan View only profile or Body Section- after all: Glen-L is selling plans not making them available as a free service online! So, I inferred from the Body Plan images about the chine's relationship to the keel.

I am remarking about this design from many (many) skiffs of my own design and building (hundreds) over the years. My remarks are intended to help 2fish to more clearly understand the garvey's performance, as drawn. She will be very agile, and I was hoping to express a subtle modification to the lines that could make her more stable at higher speeds- less sensitive in turning but not make more than a few inches change in her plans/build/resulting construction effort.

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin

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