How to Determine Size, Dimensions, and Angle of Frames for ~18ft Runabout

Hello, I'm new here, and to boat building so please forgive my ignorance.

I'm an experienced woodworker but have questions about frame construction. I'd like to build a wooden runabout, probly around 18ft long.

1. How do I determine the chine angle? Meaning the angle joining the sides of the hull with the bottom of the boat? Pic for reference: Imgur https://imgur.com/a/L70KwoL

• Is there a standard angle for runabouts?
• Are the angles the same for each piece of the frame?

2. How do I determine the length of each individual section/piece of wood for the respective frames?
Pic for reference: Imgur https://imgur.com/a/xhKnStR

Thank you for any help. I'm sure I'll be back with more questions.

 

Bard, that is a lot of questions rolled into only a few. . There is no standard angle for chine...(bottom to side intersection) In fact there are many boats that have vertical sides. Those with angled sides are likely to pick up resistance to heeling (leaning over sideways) a little more rapidly than the ones with smaller or no angle at all. That is not the defining reason for what we generally call "flare". Part of the reason is that we have been, by tradition, caused to believe that there must be some flare in the sides in order to look "Boaty". Flare toward the front end of the boat is useful to help eliminate some of the spray or splash that might find its' way into the passenger compartment. The Gentleman's runabout style ( Chris Craft, Century, Riva, and others) often have some tumble home in the sides, near the back of the boat. Tumblehome is when the sides lean in toward the inside of the boat. The opposite of flare.

Calculating the length of the frame components is just basic carpentry. The frames are usually different at each location so individual measuring is the norm.

Most of us will urge you to buy a set of plans in which almost all your questions will be resolved. We can argue reliably that you will save time and money if you get some plans that are proven. Start by checking out Glen-L plans. There are many other sources to choose from but that one has a good reputation.

 

+1 re Messabout's comments above.
If you have a set of plans with offsets, you can draw them out full size (eg on a white painted plywood 'lofting' floor).
If you enjoy doing trigonometry calculations you can calculate the angles where the top and bottom parts of the frames join - but drawing them out full size would be easier really.
Some plans for sale will even include full size templates for frames and hull panels.
The cost of a set of plans will be negligible in comparison to the final cost of building your boat.
Please do have a good look around - there are so many possible suppliers out there.
Can you be a bit more specific (if possible) re your desire to build an 18' runabout? What do you want it to be capable of? Do you want to (eg) go water skiing or fishing or just general pottering - or all three?

Here are a few websites that you could have a look at initially - there are many others as well. These are just ones that I had book marked when I came across them, because I like them.

Motor Boats 16' to 20' http://www.selway-fisher.com/Mc1620.htm

These are the Glen-L boats that Messabout referred to - Boat designs for the beginning boat builder https://www.boatdesigns.com/Boat-Plans-Kits-Catalog/departments/2/

Spira Boats - Wood Boat Plans, Wooden Boat Plans https://spirainternational.com/hp_wood_boats.html

Clark Craft - Boat Plans, Boat Kits, Boat Building Supplies http://www.boatplans.com/store.php3

There are some boats around 18' in Sam Devlin's catalogue, but you have to look for them.
https://devlinboat.com/about-devlin-design-tech/devlin-design-catalog/

Gartside Boats | Power Boats https://store.gartsideboats.com/collections/power-boats

Buy Plywood Boat Plans - Build the boat you've been dreaming about! https://www.saltboatworks.com/buy-boat-plans/

This link is a bit confusing - you need to 'open up' the boat selector box to find a long lisst.
/studyplans/index.php () - Study Plans https://bateau.com/studyplans/#specs
And if you would like any endorsement for a Sea Sled, talk to Dog Cavalry on here - he is building one similar to this, but to his own design.
Texas Sled 18 (TX18) - Study Plans https://bateau.com/studyplans/TX18_study.php?prod=TX18.

 

The angle to the vertical of the topsides, and the angle to the horizontal, of the bottom, in a chined boat are not that dependent on one another. You could have two boats with identical topsides, but vastly different underbodies, without anything being "wrong" with either boat.

 

Wow. Thank you guys so much for your detailed replies. I think buying plans will be my next step.

All of this is really helpful and informative. Thank you!

 

Please do keep us updated on this thread re which boat plan you decide to purchase - or even if you have any questions before hand re pros and cons of different designs. There are so many nice boat designs out there to chose from.

Can you be a bit more specific (if possible) re your desire to build an 18' runabout? What do you want it to be capable of? Do you want to (eg) go water skiing or fishing or just general pottering - or all three?

 

Yes, of course. I want to be able to be able to take the boat out on Lake Michigan, but only on calm days. The rest of the time, I’ll be tooling around our local lake.

The two things we hope to do the most are cruising around and water skiing/tubing.

Have yet to buy plans but I will definitely keep everyone updated.

 

I would lay the lines down. You could get an approx length by the offset table figures itself, but the most accurate is when laying down the lines full size.