Hello,

Just wondered if anyone knows what the approximate angle and height of a double chine angle should be to do any good in helping to prevent slides in a turn. I am making a boat and can't do a rolled one but I can do something like in the picture. Anyone got any good thoughts on good ball park values?

I want something like a 20x60 boat with a surface drive on it. Right now I have 18 degrees and about 1.7 inches (so I can get about 60 inches wide at B with a 60" wide sheet). Anyway I'd like to know what the going trend is if possible.

Thanks in advance.

Just my initial first impressions: you might need a steeper angled step to really have enough dig to counteract slide.

Second observation: give yourself some room for error with your shearline/gunnel. Curve it a little. There's nothing worse in my opinion than miscalculating a shearline and ending up with a hog or revers curved shearline.

what program are you using by chance to draw up these designs?

The software is Pro/Engineer/Creo from PTC. It is not cheap like most good CAD programs but you can get a personal use version for $240 if you want. I have used this software as part of my job for about 15 years and I like it very much.

I would taper my chines up to the same height as the top of the braces so you can weld a full floor all the way across.

Right now the bracing from bow to stern is 1" x 2" 1/8 thk. Might be better to change it to 1.5x1.5 and then add the cross bracing for a full floor also 1.5x1.5? That would be a 3 inch thick floor. If I left the stringers at 2" then cross bracing could also be 1 inch for 3 inches...

firefly,

where are you in alaska? Im in slana alaska right in between tok and glen allen

I have been playing with the chine on mud boats for 20 + years. The first one I did looks just like your drawing and was on a 17x 50. The second one is the one on the cat five boat its anly about 1.5 . I am running a 20x60 with a 2"pad and chine just like you have drawn.

I don't think that the size matters much performance wise. The reason for the brake in the chine was to change the angle on the mudd so it would not climb up the side of the hull and create suction. I got the idea from a chip break on a lathe bit. I have used the trick chine on 3 or 4 gd longtail and 2 sd powered rigs and one keelcooled 100 hp mud boat. It worked the best on the inboard, because it was a flat slick bottom and was a 40 mph+ boat. It did not lean in the turns like most inboards do. The faster you rig runs the higher it climbs on plane the less impact the chine will have on slideing . I started doing it for the long tail rigs to help them keep going in the mud, (every time I have been stuck in a mud boat it was because the mud ran up the side and caused suction).


You are going to have to do some carefull trimming where the chine meets the begining of the rake. Putting a little taper in it may help it meet the bottom where the rake starts up. Don't fight it, you can weld a strut behind it for strength, and use a expoy puddy for fareing .


Sorry about the spelling , spell check not working.

JD

I can't believe I just went outside in the rain to measure for you. The inboard is 3" wide and and came up about 2".

The 20 x60 sd boat the break is about 5 wide and just as high. It was harder to get it to meet the bottom than the others I had done. It looks nicer but does't perform any better.

If you are just going flat on the bottom use the one on the inboard, with a 2" high stringer you will have to play with the lean and angles to get it all to meet up , you want to the floor into the crease and you won't get asmny dimples. The best results I got was with a 3/16 floor and 1/8 sides. with the thicker floor you will get a truer bottom and will not need as many stringers , the trade off on weight is not so bad. The lighter boat will run faster when new , but if it dents up or hooks up it will run slower than a heavier boat in no time at all.

JD

jd do you have some pictures for all this? Im reading and learning but I always like pictures

Thanks for all the info im watching this build close!

will the program figure weight if you punch in materials. Wiil it give lift and load capacity base on hp. My next boat if made out of al. will have a 3/16 floor with the stringers made out of 3 or 4 large v's bent into the on the bottom of the boat. I will weld a 1/8" pad across the v's to make the bottom slick, and put a T in each V to act as a stiffener. I did a rig like this for a long tail 20 years ago, it has held up good , but got a little hook because it was all 1/8.

Anybody ever thought of using spring loaded skegs on the transom, kind of like they use for sponson racing boats.

JD I really appreciate the info...and hope you did not get to wet in the rain

If you put in the density (of all the different materials you use) the program will tell you the weight and where the center of gravity is etc. It is very accurate for that sort of thing. It won't tell you how fast it is going to go though. There is software that works with this program that will do so but I don't have it. If the boat is just sitting in the water (not going anywhere) I can tell how much draft there will be and where the waterline is with a given weight etc. Once the thing starts moving I need other software that I don't have.

I still have a few things to add to the model so it is going to get heavier...right now with most of the stringers but no deck seat mounts etc. 411 lb. I expect that it is going to be around 560 lb or so when I finish modeling it...we'll see.

Right now the "B" dimension is 59 inches. So you think I should just leave it like I have it then?