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no replacement of displacement? perfect size/ least draft

21K views 199 replies 34 participants last post by  JPHolla  
#1 · (Edited)
So I love to get skinny. and we can all agree there are way to many factors to take into account when building a boat from scratch. but this is my estimate for boat size vs. hull thickness. Now for guys who like to get into the least amount of water possible there is no replacement of displacement. basically extra wide and light weight, but if you want it to last very long it better be tough. if you run in rocks, logs, or a river setting where you might find yourself on a dumped piece of steel you better hope you've got a thick enough hull to stand up to the torcher.

For this theory/ draft estimate I will be comparing 3 hulls and 3 different hull thicknesses. all boats will have 32" deep sides and 72" floor with a 102"beam. keep in mind the density of fresh water requires 62.4sq/ft^3. so for every cubic ft of displacement it will float 62.4lbs.

displacements @ 8" deep.
1672-48.8 ft^3
1872-58.6 ft^3
2072-65.6 ft^3

given these displacement estimates multiply by 62.4lbs
1672-3045#
1872-3657#
2072-4094#

this means that every hull will displace that amount of weight @ 8" deep.

now lets explore hull weights. we all know most boats are .100 but a few make a .125 hull and evry once in a great while you will find a .190 witch one is best?
for these examples I estimated sqft of hull skin then multiplied by what each thickness of material weights. to keep it simple I divided total sqft and converted to how many 4x8' sheets each requires.

all weights are for 5052 aluminum sheet .100-45.7lb --- .125-57lb --- .190-84lb
16'= 5.36 sheets ---- ---- .100/ 245lbs ---- .125/ 306lbs ---- .190/ 451lbs
18'=6.01sheets ---- ---- .100/ 275 ---- .125/ 343 ---- .190/ 505
20'=6.67sheets ---- ---- .100/ 305 ---- .125/ 381 ---- .190/ 561

now that's just the skin, no frame work. So I come up with a flat rate to estimate interiors.
.100skin add 500lbs for frame work and interior of a 20' boat. for 18' on each thickness I will subtract 50# and for 16' subtract 100#

boat length- 16' 18' 20'
.100 245/645 275/725 305/805
.125 306/606 343/693 381/781
.190 451/651 505/755 561/861

^^^that is skin weight / full hull weight with interior.^^^

I come up with that rate of interior framing with the thought that the thinner the material the more frame work required. I may have went a little heavy, you decide.

so what is the best hull? would love to hear your opinion even if you don't like the last section about interior weight and think it might be off.



 
#77 ·
thanks guys. yea if I do this im gonna do it "kajun" style and spend the month of march behind a welding helmet. worst part is to create funds ill have to sale my current boat to afford a new welder and $4000 of metal. im dreaming, and im scared to death all at the same time.



 
#80 ·
I thank you for the compliment. I am a heavy equipment operator at USGypsum. I work alone and have a area im responsible for. it leaves me a lot of time to contemplate stuff like this along with help from my wife who teaches high school math. so getting help with my trig and geometry isn't far away. Im a thinker and love to tinker, its a illness.
 
#82 ·
Buy the welder can't go wrong. The welder will pay for itself. If you have someone build you a hull it's going to cost you more than a welder and when it's done you have a hull. If you buy the welder build the hull yourself which your capable of you will have a hull and welder when your done. And the best part is if you don't like something you can tear it apart and weld it back up the way you want.
 
#88 ·
Good read brotha... and I know how you are... always wanting one boat to do it all... lets build me a 1780 troller rig... with 30 inch sides as I have always wanted to fish the river ... and you can build the baddest fan rig known to man ... and we will use yours to run the shallows and mine to bust bigheads...BOOM ... suck it math! .... just saying.. lol
 
#92 ·
The perfect size for the least draft...I'm hoping mine is.

It's a 2185 with a 102 beam sporting 28" sponsons. I floated it the other day so I could do some work on its trailer. Very ittle more than the corrugations on the bottom was submerged. If the drain plugs hadn't been located in them I could have left them out. I've since put a Yamaha F-150LB on it and still have the fan to mount so we'll see how her ass end holds up to that.

Image
 
#101 ·
I've never put my boat on a scale to give you a solid number to work with, but, loaded with gear for 4 people, 50 gal gas, cooler of beverages and a 150qt cooler of ice for the fish, she is drawing 3-4" before we climb aboard.
 
#108 ·
yes I understand that. what you may not be able to grasp is I don't live in Texas or a southern state where a Airboat is common to see or hear. I do not think I would be seen as courteous on the DNR lakes with noise running across anywhere, day or night. there is also the swamp factor. best places I know of within 100 miles of me are less than 100acres, and there are less than 10 of them. mostly I run in 2' of water with vegetation and some timber. For Indiana IMO a fan that can do what a troller caint is the perfect option. I can totally understand your bad fan experiences, but building a user friendly fan is can be done. 6 blades for noise and easy steering are a must. not arguing with you or attacking you Garrett, Im just not going that route. I just don't see a airboat being beneficial after you get over the wow factor.
 
#106 ·
Airboat airboat airboat...lol. I've had big bad fans, not even close to a airboat. Airboat is easier to drive because it'll go through and over just about anything. Game changer for our style of fishing. We fished this year with (18) 32 gallon barrels of carp ( approx 250 pounds each) during a tournament. Beast mode:D
 
#111 ·
Rambo, maybe you need a trip up here before you build. Not joking you might change your mind :pop:
 
#113 ·
lol, man this has been a weird week. that's the 4th invite ive gotten this week to fish out of state. honestly if we haven't had the wettest may and june on record the fishing would be a lot better. our best time of year is august thru October until the fall rains start. but ever since I built my boat I haven't seen "great" fishing because of long bad weather patterns or like last year I blew up my fan blades just as it started to get good. I wasn't gonna start new stuff at the end of August.
I appreciate the invite. someday I want to get up on the big lakes.
 
#114 ·
I think that we are in similar boats Rambo (pun intended). While blow boats are awesome and lots of fun, they are over kill for the waters I shoot. In fact, there are a few scenarios that the fan boats will out shine a blow boat. Down here, coastal erosion is a huge problem and the blow boats ability to run over the little dry marsh that we have is hugely frowned on. A fan boats ability to back out of a tight spot instead of just gas on it and run over something is a big plus when trying to get permission from a land owner to fish his ponds. It's kinda like someone pulling up to a farmers house asking permission to hunt his fields while his 4x4 with 44" tires and covered in mud is right behind him.
 
#115 ·
I'm with Rambo on this one. You you guys are serious about convincing him to build a blow boat, then somebody bring one to Indiana this weekend. Make sure all your insurance is paid up, and we can hit the West Fork. Airboats are freakin cool, and I would love to have one, but they are just not practical in this part of the world.
Looking forward to watching you build this boat, Rambo!
 
#122 ·
Sooo... lets build an 1880 with 30 inch sides with a jet outboard and a fan and a kicker with a place to mount the troller on the front.... BOOM!

And by "lets" I really mean you build it and I will hand you parts and drink beer and kill fish when its completed.