[whiteriverrambo]

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.

 

[whiteriverrambo]

caint help but dream of a 1672 x.125. dry hull estimate 693lbs but would float 3045lbs total and only get 8" deep. with 500lb 4 strokes, fan, fuel cell, batteries, lights ect. it would be easy to hit 2500lb though.
looking at the rest of the numbers 1000lbs of displacement difference between a 16 and a 20. although im not sure why there is 600lb dif between the 16 and 18. and the 18-20 is only 350. the rate of displacement I guess.

 

[whiteriverrambo]

if you do the math on a set of pods (witch ive never done before) it will tell you what kind of weight your gonna displace.

avg size pods are lets say 20x24 and if they sit 10" deep then 20x24x10"=4800in^3. convert it to cubic ft= 2.78
2.78x 62.4lb = 173.5lbs so a avg set of pods will allow you to move 173.5lbs from the front of the boat to the rear and it will allow for another shooter on the front deck without sitting lower.

 

[whiteriverrambo]

seaArk their MV jons with .125hulls
........... 1872mv weighs 625.
...........2072mv.........775. ........but these weights are for 28" deep sides.


now looking at alwed .100 hulls. with 25" sides
.......1870 is 585lb
........2070 is 645lb
they make a 1670 but hull and they have hulls with 29"sides but they aren't on their spread sheeet
sooo I guess in not to far off on hull weights. maybe a little heavy on the 16 and a little light on the 20s.

 

[whiteriverrambo]

looking at those factory numbers a 20 only weighs 150lbs more than a 18 but according to my displacement math it will float 350 more lbs.

-- I guess their truly is "no replacement for displacement." although im not sure where I can get some hard .190 hull numbers we can guess. a 3/16 hull is tough and if it only weights 180lbs more it truly is the best choice. And for the guys that have built 3/16bottom with 1/8" sides it looks like a very good choice too. toughness where you need it and weight where it matters.

 

[bigbend]

I agree.

 

[GaryBriggs]

caint help but dream of a 1672 x.125. dry hull estimate 693lbs but would float 3045lbs total and only get 8" deep. with 500lb 4 strokes, fan, fuel cell, batteries, lights ect. it would be easy to hit 2500lb though.
looking at the rest of the numbers 1000lbs of displacement difference between a 16 and a 20. although im not sure why there is 600lb dif between the 16 and 18. and the 18-20 is only 350. the rate of displacement I guess.

When your doing your Calcs are you figuring actual displacement or Coast Guard Rated Safe displacement?

I think most folks would be surprised how much actual displacement a small 1448 actually has.

 

[whiteriverrambo]

thinking about the perfect fan boat but its hard. the smaller the boat the more nimble, the bigger the boat the higher it will float. but on the other hand the bigger the hull the more it weighs and the more hp it requires. this was the whole reason for all the math. biggest problem is a 16' boat requires all the things a bigger boat does. guess the biggest gains in stability and displacement is width not necessarily length.
back to the math. . . .wonder if a 1680 sits higher in the water than a 1872? or some more common hull comparisons a 1672 vs a 1860.. . . . this may take a while.

 

[whiteriverrambo]

When your doing your Calcs are you figuring actual displacement or Coast Guard Rated Safe displacement?

I think most folks would be surprised how much actual displacement a small 1448 actually has.

im figuring actual volume of a specific hull displaces when it sits 8" deep. then im using the fresh water 62.4 lbs to find out what each hull will take to sit it down that deep in the water. that's how im getting my numbers. nothing to do with coastguard stuff.

for each hull I am figuring a 5' rake that comes up to 32" and im not doing the full physics to get the round oval shape displacement of the arch. im just doing basic geometry of the triangle. its only 20" of rake to come up to the 8" deep mark. I am adding the angle of the boat sides not just figuring a rectangle .

 

[kingcan]

Sooooo are you just rambling here? If you're looking for another boat thinking logically will get you to a decision faster than looking at a calculator.

Displacement and bowfishing suitability are two different subjects. An 8048 will have more displacement than a 1672 but is useless as a bowfishing boat. Stability and ability to haul a load are the two biggest factors. So you want a wide boat with tall sides. Length adds floor space and some load capacity, but isn't the biggest factor. Why do draft calculations when your boat no longer sits level because it is loaded with equipment and people? Think about how many people you like to fish, how many fish you're planning on shooting, and type of water you shoot most often.

 

[whiteriverrambo]

Sooooo are you just rambling here? If you're looking for another boat thinking logically will get you to a decision faster than looking at a calculator.

Displacement and bowfishing suitability are two different subjects. An 8048 will have more displacement than a 1672 but is useless as a bowfishing boat. Stability and ability to haul a load are the two biggest factors. So you want a wide boat with tall sides. Length adds floor space and some load capacity, but isn't the biggest factor. Why do draft calculations when your boat no longer sits level because it is loaded with equipment and people? Think about how many people you like to fish, how many fish you're planning on shooting, and type of water you shoot most often.

good point although draft to me is very important. to me it separates the avg hull from the most capable. its all to get skinny. yes its to haul more weight but simply deeper sides will do that safer. getting a boat to sit level no matter what its length and weight is a art form. every boat can be adjusted to sit level.

 

[CarpCommander]

I agree with kingcan-toss the calculator in the toilet. You're over thinking things brother.

Why are you obsessed with shallow draft? Most BIG fish I've shot have been in 2-4ft of water. Skinny water usually equals skinny fish. Unless you're talking a numbers tourny, in which case you'll get spanked by airboats 90% of the time.

To cover all bases, you really need several boats. That's not reality for most of us though, so get what fits your needs and style best. For me that's an 1872 kicker rig, with distant future plans for a 2 man mini airboat for local marshes. Itlł be different for everyone though. But general use, with a troller, fan, or kicker, 1872 is hard to beat.

 

[whiteriverrambo]

actually KINGCAN- you bring up a good point after sitting here I realized I never really made it clear my intentions for doing the math. your right I didn't bring up or make any real point. so here goes.

you think about a bowfishing boat you need width for stability and depth for safety. but also you need to think about water depth it will float a load in, trailering weights, trollingmotor stress, layout, prop or jet, ect. This is some of the things going through my mind as I dream of a bigger craft. I don't want it huge but safe and capable. I know a typical guy would just go buy the biggest he could afford but I was gonna put all my cards on the table on this one and think about every single detail. basis and rules of engagement is fan boat that floats skinny and handles deep water well. deep sides, large hp, that runs 40 empty and 30 loaded no mater what.

 

[CarpCommander]

What you describe then is a 1872, with a 3/16 flat bottom, with 1/8 sides 28-30" tall, with a 150hp, pods, and a sizable fan.

Now go buy/build it

 

[mudfish]

Why Yall talking about 72 floor and 102 beam.
My airboat is 84 floor and 98 beam.
:co:

 

[mudfish]

Why Yall talking about 72 floor and 102 beam.
My airboat is 84 floor and 98 beam.
:co:

 

[whiteriverrambo]

What you describe then is a 1872, with a 3/16 flat bottom, with 1/8 sides 28-30" tall, with a 150hp, pods, and a sizable fan.

Now go buy/build it

lol yes it sure looks that way don't it. ill need you to come help me with poly.

 

[whiteriverrambo]

Why Yall talking about 72 floor and 102 beam.
My airboat is 84 floor and 98 beam.
:co:

102 is the widest allowed down the road. IMO the additional slope in the sides will add to the displacement and creating a slower rate of sink for every lb. added. only reason I was doing 72" math was to include the whole community in on the conversation. very few would be able to comment on a 84" wide barge. but I realize most have no idea what their boat even weighs.

 

[GaryBriggs]

We don't require super skinny draft in our lakes, and a boat that is to big is to difficult to turn around when we nose into tight coves.

My partner has an 1860 Prodigy with a mod motor hanging off the back, I can't tell ya how many times we've had to push pole backwards to get out. Where as my 16' with the outboard lifted out of the water was able to turn around and troll out.

I don't need more than 16', I just wish my boat was wider than 44". I kept everything as lite as possible and we regularly troll through 8" of water.

You have to appreciate Rambo's analytical aproach to these things. At a minimum it gets a good debate going.

 

[SwampyBottoms]

Don't put poly on that fan. Then your weight issue goes off the charts. Just paint it with gator glide or something like that.