Steel Boat Build

Hi everyone, this is my first post, and I have little clue as to what I am talking
about.
I installed Freeship, statred a new sketch, made my boat
5.2 meters long.
1.762 meters wide
Draft: 400mm
and hit ok.
The result was a sketch that I do not understand.
I get the length width draft and height,
bur I do not understand the brown curve with the measurements
that move around when I for example stretch the hull back and forth.
I also do not understand the greenish curves and their meaning.

I have attached the sketch in pdf format.
Perhaps someone can explain what I do not understand.
EDIT: I have also attached the resulting Design Hydrostatics
calculation if anyone cares to comment on the feasibility of this
design, the boat is for a small lake to fish from, I think it is quite
stable, and the cg and cb look good to me, but I really need opinions
as I have never had anything to do with boats other than to weld them.

I have looked on line and my horizontal centre of buoyancy is above my horizontal centre of gravity,
is this a good thing or a bad thing, one site says its good for stability.

I look forward to your replays

Thank you kindly

Regards, john

 

Have I asked an impossible question,
Or does it simply make no sense.

Regards, john

 

Yes, your question makes sense but simply fact to make it suggests that your skills are so scarce that probably can not understand the answer.
Any way, the brown curve represents the area of the submerged portion of each frame.
I do not see any green curve. There are some blue curves representing the longitudinal sections of the ship.

 

I'm not sure what's going on either..

I think your green curves may be buttocks & your brown curve is of areas.
I have never computered design, maybe a book could help more than a program such as this https://www.amazon.com/Small-Design-Beginners-Frank-Bailey/dp/0589502034
I have it, quite nice- goes through design of small vessels.
All the best from Jeff

 

Thank you for your assumptions.
There is equal amounts of Green and Blue with a little Red in that colour,
R64-G128-B128.
As regards describing the Brown curve with the values also marked in Brown
it goes way up over the boat and thus how can it be submerged.



Regards, john

 

The curve of areas is not bounded by the hull lines.
It looks like your LCG might be a bit forward. Most boats it is about 52% to 58% of the DLWL aft of the FP (forward perpendicular - Usually station 0 at the bow.)
If this is your first 'design' you are doing quite well but you might want to get a book to help you understand what you are doing, the terminology, etc.
If this is a steel boat (your header) it will be quite a challenge to plate up. Get your English Wheel, torch, and hammers ready!

 

Greenerpastures, You're welcome. I see you know a lot about colors (not enough to design boats). As mentioned above, a good book would help you to know what you're doing. My advice is that you study the basics of naval architecture before you start designing boats.
I do not know what you think is submerged. Of course the brown curve is not.
And yes, center of buoyancy should be above center of gravity.
Regards

 

Welcome to the forum.

This is the "typical" result with basic parameters punched into free design packages, for a round bilge yacht.

The colored lines represent slices taken at default settings, through the hull. These are longitudinally, vertically and horizontally oriented. These settings can be changed, but more importantly, you need to understand a whole lot more about what's going on, than you currently do. Do yourself a big favor and open a few books on yacht design and plow through, until you have a basic grasp on the processes, then you can move onto actually modeling something with software.

Simply put, drawing some pretty pictures (that boat isn't even remotely pretty IMO) with free software doesn't mean it's a boat, nor very well suited to your needs, or even if it'll attempt to float upright on launch day. It's just a software package doing what you've asked it to do, without regard to what is appropriate, necessary, desired or needed as an end result, that you'll take farther from shore than you can swim back to.

 

Well thanks for all your help, I certainly know more now than when I started asking.

Regards, john

 

It helps a lot for a builder to have stations on even numbers. For example .5 meter or 2 feet, etc. b@stard divisions like you show makes setting stations much harder.

 

Hi John,

My wife and I are building a steel boat that she designed and planned. I added the "planned" part, as the detail drawing after the hull shape development is a big chunk of work.

I suppose you could skip this second part and traditional loft the frames, but that misses out on some of the labour savings with steel (getting it NC cut).

This is a small boat for steel, and the plate thickness will be getting thin. Perhaps a different material would be more appropriate ? I would suggest you pick up Dave Gerr's "The elements of boat strength" and have a read.

While the design and build your own boat is a possible path, it's a long one. If you just want a boat, and not the journey then think twice. I'm sure it would be cheaper to purchase a second hand boat.

Cheers,
Mark

 

A 5m boat is small for steel so the appropriate thickness shell plate might have that 'hungry horse' look from all the welding. How about aluminum????
The smallest steel boat I have designed was 7.3m and worked fairly well but the owner admitted that in the long run (5 years of maintenance and operating costs) it would have made more sense to go with aluminum.

 

Hi JSL
I agree with all you say, but this boat will be for fresh water uses, it should be easy for me to maintain for say 10 years, after that I will sell it or pass it on to someone who will use it.

I intend to use high grade steel, cold rolled, sandblast and use good paint.
I know aluminium would be much better, but am getting into welding again after a long break of 16 years, so I want to build up my skills to the appropriate level for aluminium welding, I have a mig, where as I do not have the tig required for aluminium.

I have done more research, and though I still have trouble with the terminology, I understand how it all comes together regarding stability and safety.

I am hoping to weld the boat to what ever hull structure by drilling the plates / sheets, or slotting them so that the holes / slots will meet up on the centre lines of the hull structure, so that when I tack the sheets on, I can then weld within the slots and directly onto the steel structures, thus limit the distortion.
I will then fill what ever slight cavity's are left with fibreglass and sand smooth.
This boat will be for fishing on a lake, but for the most part just and experiment that will hopefully lead to another bigger boat.

I have re modelled my original plan, as I wanted a more stable platform that the original did not provide, I will attach my results in the hope someone will comment on whether I have got worse or better, and how can I get the LCG to move back a little more, without affecting the stability and low centre of gravity I seem to have achieved.

Thank you all for commenting

Rdgards, john

 

Hi Mark, all good points, I have since found some good information regarding
the design aspect of it all, and have changed my original to what should be a somewhat more stable platform from which to fish from, I've attached them in #13, and look forward to hearing whether I have made things worse of better regarding stability.
I will also be including a small cabin up front, which will be sealed from any intake of water, via a proper fitting door
I also intend to add a deck on the aft right up to within 600mm from the cabin, this deck will be again sealed, with access via water tight hatches.
I may try to incorporate flotation under aft deck and front deck up high so it does not inter fear with buoyancy, I will even flip the boat over in the lake as I have every hope it will self upright again, and I am a firm believer in testing proving and learning from what one does.
I have so far managed to keep the centre of gravity very low, and thus increase the boats ability to resist heel and remain in the upright position quite considerably.
Someone mentioned regarding looking at my first attachments that the LCG was too far forward, I hope other will comment on this again regarding my latest attempts outlined in #13, I can't seem to move this point back without significantly altering stability and moving the LCB also back which puts the nose of the boat at risk from being pushed down too easily by a wave.

Thanks for commenting, and good luck with your boat.

Regards, john

 

Re Your comment about not having a TIG machine which is required for welding aluminum is not correct. Most aluminum boat welders use MIG for welding aluminum boats with skin thicknesses down to .125 inches ( some even to .100 but the distortion becomes an issue)

You mention round bilge and stability. A hard chined hull will normally provide more roll stability than a round chine hull.

You should send us a cross section of your hull. In steel or aluminum, you have to have developable shapes for the sheet to conform to. (without rolling equipment and a lot of talent)

So if you are wanting to have a round shape, it will turn into a multichine cross section

Aluminum vs Steel
Aluminum is more expensive, no doubt about it, but the ease of working with it more than compensates for the additional expense. Most wood working tools can cut it with ease. And if your plan is to sell it in 10 years, you will always get more out of an aluminum boat.

And weight is an issue as well