Landon's 1/10th Scale FS19 Model

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Fuzz
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Re: Landon's 1/10th Scale FS19 Model

Post by Fuzz » Wed Jan 11, 2017 3:05 pm

I believe your thinking is correct but I am not sure.
Post this question with what you have done here in the power boat section. JM does not always check this section but he looks at that one. Best to get the correct answer from him.



silentneko
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Re: Landon's 1/10th Scale FS19 Model

Post by silentneko » Thu Jan 12, 2017 8:53 am

A few things to note, some of it you seem to have been pressing on, I may not get it all correct, but if not someone will chime in.

Plywood and foam thicknesses do not exactly exchange. I was told a while back that to replace plywood with composite core you need to multiply the thickness by at least 1.5 and round up. So if you are using 1/2" plywood, then you would need 3/4" foam core. If using 3/8" ply then you would need 5/8" foam core............

Also, and I can tell you this from person experiments, you need more glass on foam core for puncture resistance. With plywood decks you might be able to get away with a layer of 6oz cloth, but on foam core you will probably need at least double that.

Once you add all that up you will see the weights are not far off. That's the reason they say it's not worth it to build a smaller boat with the more expensive composites.
Built: 15ft Skiff, 16ft Skiff, Modified Cheap Canoe.....FS17 coming soon!

jorgepease
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Re: Landon's 1/10th Scale FS19 Model

Post by jorgepease » Thu Jan 12, 2017 6:32 pm

I will chime in since I have a little experience on foam.

I find foam core to be much stiffer and can still be lighter than ply of equal thickness depending on your laminate schedule. I was able to use less framing and span larger distances which saved weight but it all depends on the design. My boat is all foam but I went kind of heavy on the glass for the hull so I don't think I saved much weight.

I built an XF20 and that huge flat bottom needs weight or else you pound a lot. The more weight I have on that boat the better it rides. I noticed that my speed doesn't change much either loaded or light, because it's form drag which seems to be more important. My top speed with good conditions is 36 mph alone and I lose maybe 3 mph with 5 more people on board. I'm also propped for low and midrange because any faster and that boat is out of control.

The point I guess is, I wouldn't get too hung up on weight, 50 or 100 pounds either way is not going to make a huge difference in speed but could help you in comfort.

TomW1
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Re: Landon's 1/10th Scale FS19 Model

Post by TomW1 » Thu Jan 12, 2017 7:38 pm

narfi wrote:ok, i checked out that calculator and now I am really confused......

I entered 12oz cloth, 36inches by 1yrd (1sq yard) and 50% resin, it gave me an answer of .75lbs which is 1/2 of what I expected.......

I thought that if 50% epoxy then the epoxy weight would be the same as the cloth weight, making the math 12oz + 12oz which is 1.5lbs or 1/2 of the answer I received......

What am I doing wrong?
I thought cloth weight was the weight of one yard by one yard? is that wrong?
Is my understanding of resin ratio wrong?
Narfi a yard of cloth is 50" wide x 36" long so that is your error. So when you lay out your cloth on your boat you will have enough to cover the bottom over the chine and up the sides a few inches.
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

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Re: Landon's 1/10th Scale FS19 Model

Post by TomW1 » Thu Jan 12, 2017 8:07 pm

narfi wrote:Ok, so I found this quote by Jacquesmm
jacquesmm wrote: Anyway, using my table, to replace the 12 mm ply, I get 5/8 core with 20 oz. each side which is very close to the K. Hughes table.
So, use a 5/8 core with on each side, one layer biaxial 45/45 12 oz. and one layer of our 9 or 10 oz. woven.
If you want to do it in one shot: one layer 1708 each side is fine. It's only a sole.

I did the math with a standard span of 24x36" edge supported, loaded with 4 men, 35 mph in a chop and get the same result or a littler less.
I do not understand the differences in needs for weights of foam, but they do mention using H45 in that thread, so using those weights to replace the 1/2 inch plywood.........

5/8" H45 nidacore is .18lbs per sq foot
22 oz worth of cloth on each side (12+10) = 44 + 44 in resin = 88 /9 = .611 lbs of glass/resin

.611 + .18 = just under .8lbs per sq foot compared to the 1.25lbs for 1/2" Okume is a savings of .45lbs per sq foot not considering the weight the sealing epoxy you would need to put on the bare wood.

Using one layer of 1708 on each side of 5/8" H45 comes to .875lbs sqft or a savings of .375lbs over 1/2 Okume
If your using 1708 double or even triple your epoxy use. First you have to saturate the 8oz. mat then instead of 12oz. biaxial you are filling 17oz. biaxial. Don't forget your cloth per yard is 50x36.
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

narfi
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Re: Landon's 1/10th Scale FS19 Model

Post by narfi » Thu Jan 12, 2017 8:41 pm

TomW1 wrote:
Narfi a yard of cloth is 50" wide x 36" long so that is your error. So when you lay out your cloth on your boat you will have enough to cover the bottom over the chine and up the sides a few inches.
I understand that, but thought that the weight classification was for 1 square yard?
12oz cloth is weights 12oz for a 36"x36" peice, a 6oz cloth will weight 6oz for a sq yard, etc....??

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Re: Landon's 1/10th Scale FS19 Model

Post by narfi » Thu Jan 12, 2017 8:49 pm

Wont have time to study (play) with this for the weekend, Flying into town with Landon to get his passport done. (cruising to mexico in the spring!)
Taking him to an Aces game and some fun stuff, then way too much shopping :(

I think I have asked enough stupid questions, now I just need to sit down and do some basic math and rough estimates on weights to see what sort of room I have to play with.... Next week!

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Re: Landon's 1/10th Scale FS19 Model

Post by narfi » Thu Jan 19, 2017 11:31 am

Ok. I'm an idiot.....

Had to get up early to check generators this morning and had an hour before work so I dug the model out and a steel rule to take measurements......

I built the hull fine to scale as the plans are in inches I just decided inches by 10.
However when I started laying in the cardboard template layout ideas my brain skipped a cog and started thinking 1/10 of a foot was 1 inch. Obviously an inch is 1/12 an inch...... oops...

No harm done. It was just cardboard and tape. But I feel about as stupid as mixing the 3:1 epoxy at 3:2 and not knowing why it wouldn't cure......

Amazing how the brain works, once you are convinced of something you never question it again and thus begins a series of mistakes you should be doubting and checking but arent.

I really like the clean computer drawings the guy is doing for fs17 layout ideas. I might have to learn how to do that.....

Calculations I did yesterday based on my bad math ended up with a total weight of 1500lbs with this layout in foam with foam sole. And 1650 in plywood and plywood sole.

That's including 365lb motor and 40gal of fuel, 20lb tank (Probably high estimate??) a 100lb battery and cables and 50lbs of electronics etc... in the console.

My guess is the foam estimate is a bit low and plywood is a bit high so really you were all right that the difference is fairly small. However I was also correct that if I want that much stuff and come in around 1500lbs allowing for 1000lbs of people + gear I would need to use foam or some other means of lightning the project.

For this example comparing 1500 and 1650 is fairly close but the difference between 1000 and 850 usable is significant.

Will work more on figures using better math this time....

Fuzz
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Re: Landon's 1/10th Scale FS19 Model

Post by Fuzz » Thu Jan 19, 2017 1:12 pm

My dory weighted 1750 all up. 50HP outboard, 5 HP kicker, gas and all the other stuff included. I have run it with well over 1000 lbs of people in it and still ran in the low 20s. I know the dory is a bigger boat but all in all I think they are pretty close to each other.

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Re: Landon's 1/10th Scale FS19 Model

Post by narfi » Fri Jan 20, 2017 2:08 pm

Which Dory did you make? You do a build thread here about it?

I think I just figured out one of my major hickups in the learning curve....
I had it in my head that DWL was designed weight limit, but its not, its Designed Water Line........ doh!

So if the Displacement at the DWL is 2500lbs, then that means that sitting still, the bottom of the sole will be level with the water if total weight is 2500lbs and it is properly balanced?

So with the drains above the floor/sole plugged, what is a reasonable weight limit? I think maybe I was being too restrictive just by not understanding some of the basic terms o.0

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