Advise for buildin aluminium hull.

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southern safaris
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Re: Advise for buildin aluminium hull.

Postby southern safaris » Tue Aug 21, 2018 1:15 pm

220 gpu top pic and Suzuki 1.3l on a 14' hull bottom pic
And what the round sides look like (not trying to talk you into one at all) just a reference, and if you break the sides and put in a turn chine in bottom of hull you can go much wider as stated prevoiusly so dont get stuck on that 60" of flatbottom at the bottom of transom, theres actually about 72" flatbottom moving forward in the hull.... that was just a reference to my bottoms on my type hulls , a hard chine hull should have more flatbottom if i were building it
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Anthony Hughes
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Aluminum round-sided hulls

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Re: Advise for buildin aluminium hull.

Postby southern safaris » Tue Aug 21, 2018 1:17 pm

Running 73" 3 blade like you pictured
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Re: Advise for buildin aluminium hull.

Postby M0RYAK » Tue Aug 21, 2018 5:11 pm

southern safaris wrote:220 gpu top pic and Suzuki 1.3l on a 14' hull bottom pic
And what the round sides look like (not trying to talk you into one at all) just a reference, and if you break the sides and put in a turn chine in bottom of hull you can go much wider as stated prevoiusly so dont get stuck on that 60" of flatbottom at the bottom of transom, theres actually about 72" flatbottom moving forward in the hull.... that was just a reference to my bottoms on my type hulls , a hard chine hull should have more flatbottom if i were building it



I understood what you provide size first time for my first picture only.

I have good example from this forum (I think), look below:
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Re: Advise for buildin aluminium hull.

Postby Slidin Gator » Tue Aug 21, 2018 9:03 pm

Moryak,
Rethink your overall width. How are you going to fit a 72" prop inside of a 72" hull? Go back and re-read Mr. Hughes original input:

southern safaris wrote:I have a 14' hull ill give you some round about numbers on...

This hull was built with metal 10' wide and 14'6" long rendering a transom of 7'6"at top and hull length 14' long roughly the boat bellies to roughly 8' midship, i will try and post some pics


7' 6" = 90" width at the top of the transom. You can cheat that by a few inches with a 72" prop, depending on the cage set up, but that is about it.

There is really no need for anything other than vertical sides above the chines, so start with the width at the top of the transom, subtract the chines and your width of flat bottom and you end up with the width of angled section.

Also, for a deep water boat, there is no specific need to stick with the 11 foot length. Myself, I would be thinking 13-14 feet, but at least 12 feet. The added length will improve on the ride (you mentioned a 20 mile ride just to get there). 150 Hp from a light weight engine is plenty to run a good sized hull, as long as dry ground running is not a key goal.

Keep in mind, all of this is based on the assumption that you are running water. For me, I'm not too worried about the plants making a narrow trail, I just run them over and make the trail fit the boat. Of course it does depend on the plant type and size!

One other hull form worth considering is a step hull. Those hulls fly on water and might be just the ticket for getting to the duck blind first. But you need advice from someone other than me on the set up.
I grew up thinking I-10 was the Mason Dixon line.
1986 Airboat Engineering Inc., 14' Marsh Master. Refreshed narrow deck, SV O-540, 72” NGQ. A Bob Stossel original.

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Re: Advise for buildin aluminium hull.

Postby southern safaris » Tue Aug 21, 2018 10:21 pm

I agree with slidin ... but also keep in mind that i usually swing a prop roughly 4-6"down inside the hull so when you raise your motor to that aspect the circumference of the overall diameter of the propeller thats swinging is raised so your only getting a percentage of that 72" (proposed prop length) swinging between the gunnels..... if the center of the prop was theoretically even with your gunnel height, then clearance would be an issue but since it has to be raised to ? # of inches then clearance grows and this allows for larger props to be cleared.... ie the last carmotor boat i built had a 82.5" prop swinging comfortably in a 7'6" transom boat with room to put walk arounds and exhaust in .... but everyones set up is different i hope i conveyed the proper thoughts .... im a horrible teacher and even worse at explaining sorry
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Re: Advise for buildin aluminium hull.

Postby M0RYAK » Wed Aug 22, 2018 7:06 am

Thanks for correction! Off corse i will make top of transom with width more them prop.

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Re: Advise for buildin aluminium hull.

Postby M0RYAK » Wed Aug 22, 2018 7:17 am

Condition of using. (my freind's videos).




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Re: Advise for buildin aluminium hull.

Postby M0RYAK » Wed Aug 22, 2018 8:16 am

What for some hulls have small bends of bottom on each sides and some only partly? Is it important for my?
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Re: Advise for buildin aluminium hull.

Postby M0RYAK » Wed Aug 22, 2018 11:28 am

[quote="Slidin Gator"]Moryak,


There is really no need for anything other than vertical sides above the chines, so start with the width at the top of the transom, subtract the chines and your width of flat bottom and you end up with the width of angled section.


Is there a law for the difference between top of thetransom and width of the flat bottom on transom, if hull with chines?

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Re: Advise for buildin aluminium hull.

Postby Slidin Gator » Thu Aug 23, 2018 1:09 am

Moryak,
Before going any further, you need to decide which situation is more important, the first video of your buddies boat getting stuck in the tall grass or the second (and previous) showing a need to run open, choppy water. A wider hull is generally best for either option, but the hull form and other decisions are different.

Either way, the narrow hull is a poor performer in the tall grass for sure. Narrow hulls are great for outboard and mud boats, anything that needs to push on the water for power needs to stay in the water for the motor to grab, so the narrow hull form presents the minimum drag.

An airboat, while liking some water to keep the friction down, does not need it for propulsion. A properly set up, wider hull (like the round sided boats Mr. Hughes is generously showing), with appropriate power, will jump up on top of the brown stuff in that video and run like the wind a good 1 foot above what the boat in that video is doing, that is if you are willing to keep the hammer down. An airboat is just a bit shy of flying when running in it's element, the problem is when they actually do try to fly :!:

So back up to the beginning, if you have 20 miles of river/canal to run to the duck blind, how many miles would it be if you cut straight through the tall grass? If the answer is a whole lot less, then you want a boat that will make a trail through the thick stuff so eventually your buddy in the narrow hull can follow and you guys can hang out a while longer at the big floating chicken ranch, get one more coffee etc. and still be first to the blinds. Plus, you can approach the blinds from the grass, never even running the deeper water off the beach and spooking the birds you are looking to shoot at first light. Then, it's 15-20 minutes back for lunch to decide what to do that afternoon.
I grew up thinking I-10 was the Mason Dixon line.
1986 Airboat Engineering Inc., 14' Marsh Master. Refreshed narrow deck, SV O-540, 72” NGQ. A Bob Stossel original.

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Re: Advise for buildin aluminium hull.

Postby M0RYAK » Thu Aug 23, 2018 4:51 am

I don't like to make the airbot like my friend, i'd like to do it like your and get more information about properly and safely size of a boa, known HP and weight of air boat with crew. Also my purpose to get a airboat witch cans to follow throught the shellow water without problem (20 miles thought River and after than 20 miles with depth 0,5 metrs, where simetimes i will met small places ( 100metrs) with depth about 2" or mad without water under keel. That way witch was created by my friend throught the tall grass about 200 metrs. It's not more mportant purpuse for me.

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Re: Advise for buildin aluminium hull.

Postby Slidin Gator » Thu Aug 23, 2018 10:53 am

Moryak,

Just checking to make sure this is heading down the correct path, it sounds like we are.

On your first question about the bottom form, go with the upper picture with the bend in the rear but blending into flat hull up front. If you study the round sided hull information, you are simply replacing the round (soft chine) area with a diagonal and hard chine section.

I don't really understand the second question:
M0RYAK wrote:Is there a law for the difference between top of the transom and width of the flat bottom on transom, if hull with chines?

Are you asking about transom height or width? Height no, there is no specific relationship. Width, the top of the transom is just simply the widest part of the hull.

Find out the size of the material you can purchase locally, that is part of what drives the hull design.
I grew up thinking I-10 was the Mason Dixon line.
1986 Airboat Engineering Inc., 14' Marsh Master. Refreshed narrow deck, SV O-540, 72” NGQ. A Bob Stossel original.

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Re: Advise for buildin aluminium hull.

Postby M0RYAK » Thu Aug 23, 2018 2:35 pm

I am asking about relationship beetwen lenth of top transom and lenth stright line down part of the transom (without angles). Marked green lines.

I can purchase next sheets with size 13'4"x5' or 20'x6'8" type 5083.
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Re: Advise for buildin aluminium hull.

Postby M0RYAK » Thu Aug 23, 2018 3:22 pm

You advise wider hull. But how correct choose of width aft flat bottom if weight of airboat is 250 kg. with engine 150 HP? And what width of the flat bottom will be on middle?

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Re: Advise for buildin aluminium hull.

Postby Slidin Gator » Thu Aug 23, 2018 8:19 pm

Those sheet sizes are not ideal, it is better to bend the hull out of one sheet. For the hard chine hull I guess you can make seam welds right at the chine to vertical side break with some angle on the inside to re-enforce.

You want a transom overall width at the top around 86-90". As I said, make the sides vertical to the chines. Work inwards from there with the chine section and diagonal and you should be able to get more than 60" of flat at the transom.

The bare hull may be 250 kg, 550 lbs, but the grand total is going to be 1,500 lbs or more I imagine. Work your layout drawing for more detail input. I'm off line for a while, perhaps others will chime in.
I grew up thinking I-10 was the Mason Dixon line.
1986 Airboat Engineering Inc., 14' Marsh Master. Refreshed narrow deck, SV O-540, 72” NGQ. A Bob Stossel original.

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Re: Advise for buildin aluminium hull.

Postby M0RYAK » Fri Aug 24, 2018 5:11 am

Slidin Gator wrote:Those sheet sizes are not ideal, it is better to bend the hull out of one sheet. For the hard chine hull I guess you can make seam welds right at the chine to vertical side break with some angle on the inside to re-enforce.

You want a transom overall width at the top around 86-90". As I said, make the sides vertical to the chines. Work inwards from there with the chine section and diagonal and you should be able to get more than 60" of flat at the transom.

The bare hull may be 250 kg, 550 lbs, but the grand total is going to be 1,500 lbs or more I imagine. Work your layout drawing for more detail input. I'm off line for a while, perhaps others will chime in.




Thanks!

My engine wight - 190 lbs,Hull - 360 lbs, plus 2 peopls - 240 lbs each, fuel - 50 ltrs, eqipment about 100 lbs. Total about - 1200 lbs.

See below (example: how to make).
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Re: Advise for buildin aluminium hull.

Postby M0RYAK » Tue Aug 28, 2018 2:02 pm

I little be changied design 13"x 7".
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Re: Advise for buildin aluminium hull.

Postby M0RYAK » Tue Aug 28, 2018 3:05 pm

I have afraid to mistake for choose of propeller (propellers what I showed above from aircraft). I will use engine from motorcycle Honda CBR1100XX with gear box - 150 HP, max rpm 11000. I have possibility use reduction 5.1 or 3.4. I think cruise rpm will be 7000-8000, but sometimes i can increase until 11000. I have discussed on russian aircraft owners forum and some people's advice my use 2 blade wood prop about 74" or 78" (for wood prop possibility choose wide and pitch and diameter).

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Re: Advise for buildin aluminium hull.

Postby Slidin Gator » Tue Aug 28, 2018 7:57 pm

Actually, the composite propellers you showed originally looked like the better options, at least one of them looked like pusher type propellers. A 2 blade wood prop is not the preferred choice at all, unless that is all you have for options. 72" is pushing it on diameter to begin with for your power level, you definitely do not want to consider anything larger in diameter than 72". If anything you might want to see what is available down to 68 or 70 inches diameter. A wider 2 blade propeller would be the optimum choice for running through the thick stuff, but a 3-4 blade, narrow prop like you showed previously is a better option for maximum speed and general performance running open water like you describe.

As for gear ratios, consider 2,900-3,000 RPM to be the maximum speed that you want to turn a 72" propeller and choose your gearing accordingly. Using that as a basis, you can adjust RPM vs. diameter, keeping the tip speed constant. In general you do not want to exceed approximately 85% of Mach 1 at the blade tips.

The 84", 7 foot width hull you show will work, but it may require that you stick to a 70" or smaller prop. I don't see this as all bad, the 60" of flat is good for a light weight set up as you plan. Just make sure you add your prop, engine and exhaust set up into the design before settling on the hull. I will, however, point out again that a wider hull is more stable for the type of open water you plan to use the boat, a few more inches of width might be good.

Also, you show the bow necked in to 55", why do you do that? The bow width should ideally match or be close to the 71" flat width of flat hull up forward.

Finally, a bit of a disclaimer, I am not an expert on hard chine hulls. There is a lot of guessing on my part vs. the round sided hulls I am used to. So do not rely entirely on my input! :dontknow:
I grew up thinking I-10 was the Mason Dixon line.
1986 Airboat Engineering Inc., 14' Marsh Master. Refreshed narrow deck, SV O-540, 72” NGQ. A Bob Stossel original.

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Re: Advise for buildin aluminium hull.

Postby M0RYAK » Wed Aug 29, 2018 6:31 am

I think bow neck 55" for running through the thick stuff, but if it not good I increase width of bow.

I can choose any size for wood prop, but I have advice from builders of props 74", see below.
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Re: Advise for buildin aluminium hull.

Postby M0RYAK » Wed Aug 29, 2018 7:53 am

Slidin Gator wrote:Actually, the composite propellers you showed originally looked like the better options, at least one of them looked like pusher type propellers. A 2 blade wood prop is not the preferred choice at all, unless that is all you have for options. 72" is pushing it on diameter to begin with for your power level, you definitely do not want to consider anything larger in diameter than 72". If anything you might want to see what is available down to 68 or 70 inches diameter. A wider 2 blade propeller would be the optimum choice for running through the thick stuff, but a 3-4 blade, narrow prop like you showed previously is a better option for maximum speed and general performance running open water like you describe.



I have possibility choose of composite props any size and wide 5". See below.
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Re: Advise for buildin aluminium hull.

Postby Slidin Gator » Wed Aug 29, 2018 7:25 pm

M0RYAK wrote:I think bow neck 55" for running through the thick stuff, but if it not good I increase width of bow.

I can choose any size for wood prop, but I have advice from builders of props 74", see below.

The wider bow is specifically for improved performance when running the thick stuff. You want the bow and grass rake width to roughly match the width of flat bottom up forward to help lift/float the bow up over the thick stuff. The narrow bow just pushes the grass off to the sides until the hull is wedged in. Think of it like whiskers on a cat, if the bow won't fit, the stern definitely won't!

Restating one point, all (airboat) solutions work great/best in very shallow water (less than 4-6 inches), any solution works there. Focus on your need to run through the deep river and open water vs. that tall grass. You said the deep water previously, so that is the basis of the following.

Prop selection involves the same set of trade offs as the hull design, maximum push at low boat speed on dry ground or heavy vegetation vs. maximum speed on deep water:

- Wide 2 blade props for maximum push at low speed (like pushing through the grass), narrow blades with higher quantity for maximum boat speed.

- Larger diameter, lower RPM for maximum push at low speed, they grab more air and make more push, but the exit velocity is lower, just like a tug boat. Smaller diameter, higher RPM for maximum exit velocity and thrust with minimum drag at higher speed.

As for wood vs. composite, there is no comparison, stay away from wood unless you have no other choice. They used to be the only choice, but not anymore.

Given your stated goals, I lean towards the 1,800 mm (71" diameter) 3 blade composite. Gear for the 2,750 prop RPM and 11,000 engine RPM yields 4:1 gear ratio. You mentioned a gear box, what do you have in mind there? Why not belt drive?
I grew up thinking I-10 was the Mason Dixon line.
1986 Airboat Engineering Inc., 14' Marsh Master. Refreshed narrow deck, SV O-540, 72” NGQ. A Bob Stossel original.

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Re: Advise for buildin aluminium hull.

Postby M0RYAK » Thu Aug 30, 2018 6:24 am

Thank you for assistance!

[/quote]
Given your stated goals, I lean towards the 1,800 mm (71" diameter) 3 blade composite. Gear for the 2,750 prop RPM and 11,000 engine RPM yields 4:1 gear ratio. You mentioned a gear box, what do you have in mind there? Why not belt drive?[/quote]

My engine with gearbox it is easy and not expensed than engine plus belt or reduction drive.

In description for engine Honda CBR1100xx marked that max capacity available on 6000-9500 rpm. 11000 rpm red line.
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Re: Advise for buildin aluminium hull.

Postby Slidin Gator » Thu Aug 30, 2018 5:37 pm

So where is the 150 Hp figure at red line? It appears that a lower gear ratio (vs. the 4:1 I stated previously) might be better here, it looks like torque is plummeting as you approach the red line, which could kill the boat response in the normal operating range. The KL-1800 prop spec is 2250 RPM optimal and 2,750 RPM max. Using those figures, you are looking to put your cruise RPM around or below the 2250 and probably match up peak torque in the same area. I am thinking around a 3.5 ratio might be a good match. That puts peak torque at 7,500/2,143 with max prop speed at 9,625/2,750.

If you went 4:1 you would put optimum prop efficiency at 9,000/2,250. This would let you spin easily to red line, but moves peak torque down much lower - 7,500/1,875.

3.5 ratio will be a better gear for the long haul, open water runs that you have planned. 4:1 ratio will give you maximum performance, but your cruise is going to be at continuous high revs.

I also note the 137 Hp engine figure puts you right in the sweet range of the 120-150 Hp rating of the prop, so that is good.

How easy is it to change gear ratios in your plan? Are you just thinking of using the gear box off the motorcycle? If you can provide some details on this item it would be of interest.

I will be off line until Monday.
I grew up thinking I-10 was the Mason Dixon line.
1986 Airboat Engineering Inc., 14' Marsh Master. Refreshed narrow deck, SV O-540, 72” NGQ. A Bob Stossel original.

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Re: Advise for buildin aluminium hull.

Postby M0RYAK » Sat Sep 01, 2018 8:05 am

Slidin Gator wrote:So where is the 150 Hp figure at red line? It appears that a lower gear ratio (vs. the 4:1 I stated previously) might be better here, it looks like torque is plummeting as you approach the red line, which could kill the boat response in the normal operating range. The KL-1800 prop spec is 2250 RPM optimal and 2,750 RPM max. Using those figures, you are looking to put your cruise RPM around or below the 2250 and probably match up peak torque in the same area. I am thinking around a 3.5 ratio might be a good match. That puts peak torque at 7,500/2,143 with max prop speed at 9,625/2,750.

If you went 4:1 you would put optimum prop efficiency at 9,000/2,250. This would let you spin easily to red line, but moves peak torque down much lower - 7,500/1,875.

3.5 ratio will be a better gear for the long haul, open water runs that you have planned. 4:1 ratio will give you maximum performance, but your cruise is going to be at continuous high revs.

I also note the 137 Hp engine figure puts you right in the sweet range of the 120-150 Hp rating of the prop, so that is good.

How easy is it to change gear ratios in your plan? Are you just thinking of using the gear box off the motorcycle? If you can provide some details on this item it would be of interest.

I will be off line until Monday.


Yes i will using the gear box off motorcycle. It is easy, before start running I can change gear ratios (optimal gear ratios 1st and 2nd).


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