Venture 14 Bow Stem Question

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UniCacher
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Joined: Sun Feb 07, 2010 12:13 pm

Venture 14 Bow Stem Question

Post by UniCacher »

I am building my first wood strip kayak, a Venture 14. I am using the offset tables in Ted Moores's book. All is well until I get to where the bow stem meets stations 1 and 2. Station 2 has the profile at 12.25" and the bow stem meets station 2 at 12". When I draw the spline for the bow stem, it is also 1/4" above the bottom of station 1. Can somebody tell me what I am doing wrong, or if there is a correction to the offset data? The stern stem fits exactly; the stem meets station 13 exactly at the bottom of the station mold.
willo
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Location: Echo Bay ON.

Post by willo »

Look in the FAQ section of the tech support. There are revised offsets listed for the stems of all the kayaks in KayakCraft. Maybe you will find your solution there.
UniCacher
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Post by UniCacher »

Thanks for the reply. I looked there already, but it does not correct the specific error that I described.
willo
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Joined: Sun Jul 15, 2007 12:48 pm
Location: Echo Bay ON.

Post by willo »

On the plans for the Venture station 2 has a height of 12.25 " and the stem station at station 2 is 11.25" . The 1" difference is to allow for the stem. The offsets are plotted to the outside of the stem so you need to take an inch off to get the shape of the stem station . I hope this clears things up. I just read the other thread you posted in the project directory and the problem became more clear to me.
UniCacher
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Joined: Sun Feb 07, 2010 12:13 pm

Post by UniCacher »

willo wrote:On the plans for the Venture station 2 has a height of 12.25 "
That's the figure I have.
and the stem station at station 2 is 11.25" .
I would infer this based on the station 2 profile. However, the offset tables I am using show a point at the 12" waterline and 7/16" (Guessing... I don't have the table in front of me right now.)

The 1" difference is to allow for the stem. The offsets are plotted to the outside of the stem so you need to take an inch off to get the shape of the stem station .
I got that. I actually had to redraft the layout because I forgot to offset the 1". However, the tables I am using show the outside of the stem with the 1" offset to the inside.
I hope this clears things up. I just read the other thread you posted in the project directory and the problem became more clear to me.
Alas, I'm still not set. Perhaps I'm too OCD about this. Can I send you my drawing to clarify what I'm describing? The secondary problem is that station 1 is also below the spline curve created by connecting the stem points. If you're willing, send me your e-mail and I'll respond with the drawings.

It's raining today and I'm dying to get started on this!
willo
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Location: Echo Bay ON.

Post by willo »

I am not an expert at lofting, thats why I have 5 sets of purchased plans, but have lofted a set for experience. Maybe Glen can help you , doesn't seem to be around today. The plans show the height of station 1 to be 5/8" above the 10" water line. This puts it above the inside stem profile. Sorry I can't be more help .
UniCacher
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Post by UniCacher »

In the absence of any other help, would you look at your printed plans for me:
1) What is the waterline depth at the center profile of station 2?
2) What is the waterline depth at the center profile of station 1?
3) On the bow stem mold, from the 0" waterline reference, where does the outside of the inner stem cross station 2?
4) On the bow stem mold, from the 0" waterline reference, where does the outside of the inner stem cross station 1?

In the 1999 printing, both 1&3 and 2&4 are 1/4" off. They should be identical. I don't know which one to adjust without affecting the overall fairness.
willo
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Location: Echo Bay ON.

Post by willo »

the depth of station 2 is 12.25" station 1 is 10+5/8 " At station 2 the water line at outside of the inside stem is 12.25" The outside of the inner stem is even with station 2. At station 1 the outside of the stem cross at 10.5 ". I think station 1 is confusing you. Just ignore it for now, it is not needed to plot the stem.
UniCacher
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Joined: Sun Feb 07, 2010 12:13 pm

Post by UniCacher »

Okay, I'm going to unleash a bit of my OCD side here. I truly appreciate the help, but somehow I'm not making my point. When Ted Moores talks about tolerances inside 1/16 of an inch and I see this whopping 1/4" gap, I get a bit edgy.

Soooo....

I tweaked my plans a bit to illustrate what I'm describing. Green lines are station 2, including extension lines and reference points. Blue is station 1. Red is the bow stem. The gray line and associated points are the curve in question. It's a bit jumbled because I have 3 individual layers present.

With respect to the illustration below (click to enlarge):

#1) Station 2 crosses center profile at 12-1/4" waterline.
#2) Bow stem intersects station 2 at 12" waterline-- 1/4" above station 2. The offset is actually 7/16" from station 2 at the 12" waterline, but the spline is so flat at that point that it's nigh impossible to imagine a workable curve!


I know this isn't right, because the corresponding points in the stern line up perfectly!

#3) The lowest point of station 1 is at 10-11/16".
#4) Although there is no point on the bow stem on that vertical line, you can see that the spline crosses 1/4" above station 1. Since the bow stem crosses both stations exactly 1/4" above, it seems that the error is in the bow stem.


Image

Now, the fixer in me says just shift that whole bow stem layer down 1/4" and be done with it. However, I don't have enough confidence in my 3-D modeling skills to know that it won't create a concave spot somewhere.

I have checked and rechecked my figures dozens of times in the last two days and I cannot resolve this error! With no disrespect to the author, I believe there is an error in the offset tables.

Any help is truly appreciated!

Erich Schneider
Gresham, OR
willo
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Location: Echo Bay ON.

Post by willo »

I hear your pain! You know that the stem will cross at the same point that station 2 does so that is where your curve will start. I agree that there seems to be an error at the 12" waterline , 3/8" wont work , the plans showit should be 3 ", I just drew the stem up with the offsets given here www.bearmountainboats.com/0-kayakstems.htm . And like I said before ignore station 1 for now and keep in mind the error.
UniCacher
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Joined: Sun Feb 07, 2010 12:13 pm

Post by UniCacher »

Thanks, Willo, for the encouragement. I'm not sure how to ignore station 1. Sooner or later, I'll have to make those two lines cross. If I move station 1 up, then the sheer line and deck line get tweaked. If I move the stem down, then the bow point moves down. I thought about stretching it, keeping the fore point fixed, but that won't work, as stations 1&2 are both 1/4" off.

I am crossing my fingers that I hear back from BMK with a correction!
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Glen Smith
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Post by Glen Smith »

You are using autocad to do the lofting. Please describe the size and shape of your inner stem as in is it 1" X 1" or have you tapered the leading edge?
UniCacher
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Post by UniCacher »

The stem is marked by points derived from the offset tables, visible on the drawing. The inner stem is derived by using the offset function at 1". The inner stem will be tapered to meet a fair curve from the station molds to the line described by the stem offsets.

Would it be helpful to send the actual dwg file?
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Glen Smith
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Post by Glen Smith »

I know nothing about autocad but this is my point: The inner stem starts at 1" width, the face of it gets tapered to a leading edge of 1/8" and the trailing edge varies in width from about 5/8" to 1". Can you really emulate this in autocad?

I have lofted and built a Venture several years ago. I had no problems with the lofting. I may have reshaped or displaced station 1 to get fair lines but I don't remember. I would have to dig through my hard to reach pile of forms to find the Venture ones so I can see if I modified anything. That won't get done today.
UniCacher
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Joined: Sun Feb 07, 2010 12:13 pm

Post by UniCacher »

Glen,

Understood about the buried forms. I may have to resign myself to release my grip on hard numbers and just use some good old trial and error. I'll hold out until the weekend in hopes of a more definitive answer.

All I'm using AutoCAD for is to create the 2-D drawings. I don't have the wherewithal to go 3-D with it yet. Maybe another year. The lines from the drawings are points of intersection, so any board thicknesses will be compensated for when the molds are set in place. This will be my first boat, so I'm hoping to have things as perfect as I can going in so that the inevitable mistakes won't have a head start!
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