topic Lofting a model boat hull in Fusion Design, Validate & Document Forum

Lofting a model boat hull

colin_12x12 — Sat, 03 Oct 2026 09:52:01 GMT

Please, can anyone tell me how I can create the hull shape for the attached model boat hull ? The various "Frames" created from the original paper plans are not very accurate, which is why I am trying to use the best fit Frames (21, 35, and 52) along with the "rails" I have created. My problem is that I cannot "Loft" the shapes into the bow and stern.

Re: Lofting a model boat hull

davebYYPCU — Sat, 03 Oct 2026 12:54:29 GMT

You have so many duplicate sketch (straight) lines immediately below the top sketch.

The work around small rectangle has no use in the Loft that does work. Sorted with your file. Your file has far too many sketch points in the profiles.

Edit the keel sketch to have only one straight line near the deck.

Use the solid face of Loft 1, to the Bow and Stern points. 3 Rails when the keel sketch is fixed.

Re: Lofting a model boat hull

colin_12x12 — Sat, 03 Oct 2026 13:16:09 GMT

Thanks. I'll give your ideas a try.

Re: Lofting a model boat hull

Drewpan — Sun, 04 Oct 2026 02:15:14 GMT

Hi,

You seem to be working Hard not Easy. If you build from the inside out on a model,

which is the traditional way you would do it for real or a proper model, then you

will struggle to make it fit properly unless you put in a huge amount of work. There

is a better way - model outside in.

This method involves making the OUTSIDE of the model in a solid piece and then

building the insides in a step by step way. Everything fits nicely and it is much

quicker and easier.

I am more of an aeroplane guy than a boat guy but the principle is identical and I

have modelled both exactly the same way.

First, if you have three view drawings or images then set these up on your three

basic planes and scale them and use them for a guide when modelling. These

canvases are used as a Guide and make the Model much more accurately and

faster since you only have to line up with the Canvas (that is why position and

scaling is important).

The important thing here is to pick a common point and line all of the canvases up

to that point - AFTER you have Scaled them - so that everything is in the right place.

There are a number of tools to download for aeroplane wings and airfoils so getting

complex wing shapes can be pretty easy. Lofting a Boat is much easier. With the Spline

command most boat hulls can be drawn in three or four points (three is better). With

all splines less is more. The more points you have the harder it is to get smooth

geometry and often causes beginners problems.

Work Smart and not Hard. Symmetry is your friend.

Don't try to build the whole boat when drawing half works just as well. Do all the

Symmetrical bits and then Mirror it to finish it off. In this example with an aircraft simply

model one side for the same reason.

Starting with the wing, model it solid first. I used an airfoil plugin to get my basic wing.

Now that I have the basic Outside shape I can use it to create the inside stuff. In this case

the design will be a Radio Controlled Model and since it is of largish size it will need a wing

skin of about 3mm. To create the skin I simply go to the Surface Tools, create a surface of

the wing; thicken it to 3mm; then use this thickened surface as a Cutting Tool to remove this

much of my core wing Body (and Keep Tools). Now I have the Skin Body and the Core Body.

Now I need to create the Ribs and Spars of the internal structure of my Wing. In a Boat this

would be the Frames but the principle here is Identical. Start by drawing a Sketch under the

Body I want to cut. Create a long narrow rectangle that is the width of the Rib or Frame and

make sure it extends through ALL of the body you want to cut. It doesn't matter how big it is

as we are generating another Cutting Tool. Under "normal" circumstances I would not

recommend the next step but in this case it is ok because I know it is both simple and easy

and correct usage of the technique. You have a single (fully constrained) narrow rectangle.

Using the Rectangular Pattern in the Sketch, create a number of copies of the rectangular

tool at the spaces that you want your Ribs or Frames to be. It should end up looking like this.

You will notice that mine has some black and blue boxes. This is just me being lazy

and not fully constraining one of my sketches but this particular model was done a

LONG time ago and I now know much better. The important thing here is I now have

my Cutting Tools ready.

Using the Extrude Command, select all of the rectangles in the sketch, turn on the

Core you want to Cut and set the Cutting Operation to Intersect.

What you get left with is a whole bunch of thin slices of the Core, which you want,

and the rest goes away.

In this case it was convenient for me to cut the Mass Reduction holes before I did

the cutting of the Ribs. If you need this for your Boat you can do it when it is

convenient. I simply drew two sketches and Lofted between them.

You could use a similar technique for the Spars or you could Model them. For

convenience I found it easier to model them in this instance.

I have learned a significant amount about fusion since I did this Model about

four years ago. I would do some techniques differently today but I would

definitely use this method for the basic Outside In parts of the Build.

This whole process took me about 15 minutes to start a new aircraft Model; set

it up; create the basic Fuselage and the Wing with all of the internal structure.

That was MUCH faster than my initial attempt at trying to create all the internals

first and then the outside stuff.

Cheers

Andrew

Re: Lofting a model boat hull

colin_12x12 — Sun, 04 Oct 2026 05:46:09 GMT

Thanks Andrew. I have watched several YouTube videos that have shown what
you are describing and am beginning to understand the process. One of my
problems is that the plans I am using are from 1901 and whatever copying
processes they have been through before arriving with me has resulted in a
lot of inaccuracy and distortion. Trying to get the image for the canvas
looks almost as bad as trying to model the thing in Fusion.
I will try drafting my own paper version of the plans and importing them to
see how I get on. Thanks again for assisting me with this project.
Regards,
Colin.

Re: Lofting a model boat hull

davebYYPCU — Sun, 04 Oct 2026 07:38:03 GMT

Huh? I will try drafting my own paper version of the plans and importing them to
see how I get on.

What makes you think doing it twice is a beneficial tactic?

Why would you prepare paper copies of incorrect data to import and duplicate again in Fusion.

Surely using Fusion to eliminate the paper preparation is why you are drafting models in Fusion.

That said it is your Fusion work that is hindering efficiency You have this profile, mirrored the errors on one side are purposefully duplicated.

You have the beam dimension, and the draft dimension. (Top and Bottom point easy to obtain - the hard part, placing the midpoint.)

In the pic, I used the Curvature Comb Display to show that your curves have two points that fall under the ideal outline.

By comparison a 3-point spline, (deck, keel and midpoint) I traced over your work, using 3 of your points, is going to assist Fusion to produce smooth surfaces.

Smooth consistent red curves are much better than zig zaging.

A model only 2 metres long is (not) a full-sized replica? Don't place too much attention to copies of copies, basic overall dimensions are written and no need to trace.

I didn't see anything to suggest you are working inside > out, apart from the deck and keel sketches are constructed after the frames. (backwards)

Can you argue a half ellipse is not going to work?

Brighter blue curve is half ellipse connected to the deck and keel points. Comparing Frame 52 Sketch to the ellipse.

Might help...

Re: Lofting a model boat hull

Drewpan — Sun, 04 Oct 2026 11:20:13 GMT

Hi,

As @davebYYPCU has suggested - don't make unnecessary work for yourself. If you make

what you have as your canvas then you should be able to use it as a guide to get what you

want. Remember that most boat lofts only require between three and five points and that

Less is More. A typical overhead should only need three points most often - each end and

one in the middle somewhere. As long as these splines are pretty close to the original

plans and canvas then this will be good enough. The Canvas is only a Guide, it is not meant

to be perfect. I can assure you that any Boat created in the early 1900s almost certainly

was lofted with a long flexible piece of timber and probably three nails. That is pretty much

the manual version of a Spline. I know this through experience but also as my brother is

one of the last Genuine Shipwrights in Australia and I have discussed this technique with him

many times - it is the traditional method.

Once you have the correct starter shapes then the rest should just fall into place. Most historical

techniques were learned through trial and error of what works best but almost all of them were

developed to make the job easier.

Having punched in old plans myself there is often a lot of guessing, mainly because Drafting

Standards (if there were any) have changed significantly and so interpreting some of them

are not easy. If you have exact measurements for something then use it and wing the rest. You

will almost certainly find that that is the way it was originally designed and how it was actually

built.

Cheers

Andrew

Re: Lofting a model boat hull

colin_12x12 — Sun, 04 Oct 2026 16:18:09 GMT

Thank you. As you surmised, the plans have not proved to be very accurate
(as my attempt to use the frame dimensions proved) so your suggestions of
using a "simpler" approach to get close to the "canvas" is looking like a
very sensible suggestion.
Since posting my request for help, and using the suggestions people have
made, I have managed to get a proof of concept model completed. That is
currently being produced on my 3d printer for some trials before I move on
to refining the design and making the much larger model. It's been more
than 50 years since the curator at the Greenwich National Maritime Museum
gave me the copy of the patent, so a few more months to get the model right
won't really matter.