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I have just purchased Gentry plans and am catching up on any relevant building info. I noticed you have increased the length and also had previously indicated that you had plans to place a seating cockpit in front of the engine. Would appreciate any info that you could share. Dr J

Dr J,,,, Sorry it has taken me so long to get back to you, but I just saw your question today. I did stretch the Gentry 10% between all frames with the exception of the front two (the ones that attach to the stem).. This should increase the length from 17' 4" to around 18' 7". To compensate for the additional length, it was necessary to move the motor forward some. To do this, I used a strut with a 7 1/2" drop and a 14 degree angle. This moved everything forward about 5" or so and allows me to use a 13" prop instead of a 12". There is plenty of room for the forward seating area in front of the motor. Make sure when you buy wood for battens, keel, etc. that you measure. The materials list on the plans will not work anymore once the stretch begins. My email is oldneely@verizon.net if you have questions. Fire away !!! Neel

Hi All,,, I just wanted to post a few pictures with an update. First, let me say what a wonderful time I had at G5. It was great to put faces with names. The food was great, the beer was cold, and the boats were beautiful. My three highschool buddies and I really appreciated the warm welcome we got from everyone. Thanks to the folks who brought their boats and gave out rides also. Since G5, and after the flip, I have been busy cleaning up glue blobs on the interior. Two coats of epoxy were applied to the entire interior making it a total of four or five in many areas. I have dry fitted the motor, fabricated and installed the motor beds, installed the gas tank (temporarily), and glued on the first of two laminations of the carling. The strut has been installed and the rudder is ready to go in. Other than that, I have been watching the Phillies...... Eyeryone take care....Neel

Neel wrote:
"I did stretch the Gentry 10% between all frames with the exception of the front two (the ones that attach to the stem).. This should increase the length from 17' 4" to around 18' 7". To compensate for the additional length, it was necessary to move the motor forward some."

Dont you mean you move the engine aft?

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God Bless our Troops; especially our Snipers

I would say forward.

As the boat gets longer, you would need to move the engine forward to maintain the CB

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Yes, you need to move it forward because the CB moves forward when you stretch. Exactly how much to move it becomes an educated guess, especially since I will be adding a forward seating area (more weight forward). This additional weight toward the bow is not present on the original plans. At least I think I got it right !!!! Stay tuned !!! Neel

Looking good Neel. Can't wait for a ride at G6!!!

KB

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"I'm not trying to get it perfect. I'm trying to get it finished!"
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If the stretch is only aft of stem, you have effectively added buoyancy in the aft sections. Then how does CB move forward?
Please explain.

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God Bless our Troops; especially our Snipers

I think in Neel's case, the motor is forward of the cockpit, so if he does not move the motor forward then what's the point of stretching it 10%.

Anyway, I've seen Neel and his High School buddies and they are big guys and he will need more ballast forward

David

The following drawing might help to visualize the stretch :

The Gentry profile drawing is displayed at the top. The stretched version is represented at the bottom.

• The profile drawing was cropped into two sections : body (frames 0-5) and stem (frames 5-6).
• The stem was not stretched. It was copied into the lower drawing and the body was stretched slightly.
• The stretched body is not to scale and somewhat distorted.

Note also how the boat’s center of buoyancy (CB) stays in relatively the same position :

Diagram from Changing Stock Plans by Ken Hankinson

The links below will provide more insight :

Lengthening a boat (WebLetter 38, Glen Witt)

Changing Plans (Ken Hankinson)

___________________
Paul Kane Chelsea, PQ

Building the Glen-L Hot Rod : http://www.boats.chelseacoachworks.com

Paul,
you seem to be pretty good with the computer drawing thingy.
Please take the lower drawing you have above (the stretched) and align it with the upper (original drawing). align it with the constant being the bow. (the stem sections are not stretched)
when you align both drawings even with the bow, you see how the engine moves aft.

think another way.....
1. Look at the CB of the original, see that (for sake of discussion) engine sits on frame 3.
2. Count how many frame stations get stretched aft of 3.
3. Count how many frame stations get stretched fwd of 3.
4. remember that 5 & 6 are not stretched.
5. Which end has more ADDED buoyancy to compensate for?
6. move the engine accordingly.

What am I missing here?

_________________
God Bless our Troops; especially our Snipers

You aren't missing anything ! It's a matter of perspective e.g. looking at it from the stern, CB or stem.

My drawing is a bad hack but when compared to Ken's drawing (stretched stem) it shows that many build options are available.

What is important is how the boat’s center of buoyancy (CB) is affected.

___________________
Paul Kane Chelsea, PQ

Building the Glen-L Hot Rod : http://www.boats.chelseacoachworks.com

Wow, I didn't think this would cause this much discussion. I did check with Gayle as to the placement of the motor, and her research indicated I needed to move it forward, and I don't remember exactly how much, but it was around 8" or so. That means that the CB of the motor would move that amount from the transom on the original plans. As it turns out, the aft end of the transmission ends up about 6" forward of frame #2. In the plans (unstretched), it also ends up about 6" forward of frame #2. Frame #2 on my boat is exactly 6" farther forward than frame #2 on the plans. Now, I think everything will be as clear as mud !!
Thanks for the thoughts and comments. Time will tell !! ,,,, Neel

I see. You measured from a different datum point than I was thinking of. Sorry.

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God Bless our Troops; especially our Snipers

I only hope I got it right !!! I did post a question about this somewhere on the forum, and it seemed like the right way to look at it was to take a percentage of motor placement on the plans to total length on the plans and apply that same percentage to the new length of the hull. I used the transom as the data point, but Ken, I can see your point if you start somewhere else along the longitudinal axis and use that as the data point. Neel