Preparing for GT27 build - questions

Power Boats only. Please include the boat type in your question.
wkisting
Frequent Poster
Frequent Poster
Posts: 127
Joined: Tue Jul 10, 2018 11:24 am
Location: Augusta, GA

Re: Preparing for GT27 build - questions

Post by wkisting » Fri Jan 11, 2019 7:51 pm

Jacques, any word? Are the runners a necessary/important component for the GT27? Is it possible there's information missing from the plans to describe their overall length, spacing, etc.? I can't proceed with finishing the bottom until I sort this out.


Wes
---------------------------------------------------------------------------------------------------------
My build thread is here --> viewtopic.php?f=12&t=63644

fallguy1000
Very Active Poster
Very Active Poster
Posts: 2607
Joined: Tue Jan 12, 2010 12:25 am

Re: Preparing for GT27 build - questions

Post by fallguy1000 » Fri Jan 11, 2019 8:21 pm

Pretty sure you benefit with the rubrail.

Most of the ISO and class rule crap out there would require something special at both the intersections of the horizontal hull/deck and the vertical. This is to avoid the loading of the cabin above to affect the deck. It can be managed with braces or cabinetry below, etc.

Why would you not want a rubrail? Leaving ply edges exposed is bad construction.

Where did you get the picture if not from the plans? Sometimes small, obvious stuff doesn't get a paragraph.

My plans have no narrative at all...from a different designer. An email now and then though for sure.
My boat build is here -------->

viewtopic.php?f=12&t=62495

piperdown
Very Active Poster
Very Active Poster
Posts: 575
Joined: Fri Jun 22, 2018 12:35 pm
Location: Kansas

Re: Preparing for GT27 build - questions

Post by piperdown » Fri Jan 11, 2019 8:35 pm

fallguy1000 wrote:
Fri Jan 11, 2019 8:21 pm
Pretty sure you benefit with the rubrail.

Most of the ISO and class rule crap out there would require something special at both the intersections of the horizontal hull/deck and the vertical. This is to avoid the loading of the cabin above to affect the deck. It can be managed with braces or cabinetry below, etc.

Why would you not want a rubrail? Leaving ply edges exposed is bad construction.

Where did you get the picture if not from the plans? Sometimes small, obvious stuff doesn't get a paragraph.

My plans have no narrative at all...from a different designer. An email now and then though for sure.
FG, with all respect, he mentioned rubrail only in passing. His question is whether the runners are needed and, if so, what length are they.
Eric (aka, piperdown)

"Give an Irishman lager for a month and he's a dead man. An Irishman's stomach is lined with copper, and the beer corrodes it. But whiskey polishes the copper and is the saving of him." --> Mark Twain

fallguy1000
Very Active Poster
Very Active Poster
Posts: 2607
Joined: Tue Jan 12, 2010 12:25 am

Re: Preparing for GT27 build - questions

Post by fallguy1000 » Fri Jan 11, 2019 8:49 pm

Oh right. About the runners...have you ever built a house floor? Span ratings of 3/4 ply are typically 16"...you can go up to 2', but runners are just needed opposite floor supports..

I don't have the plans for that great rig, but floor spans are needed where people will walk.

Forgive me if I am missing anything. Jacques is not going to answer everything timely...he is not sitting by the pc all day..and not sure he even uses a smartphone.

Runners help keep the vessel off the bottom and provide a wear layer. They would be considered optional by most builders and designers. A great option.
My boat build is here -------->

viewtopic.php?f=12&t=62495

wkisting
Frequent Poster
Frequent Poster
Posts: 127
Joined: Tue Jul 10, 2018 11:24 am
Location: Augusta, GA

Re: Preparing for GT27 build - questions

Post by wkisting » Fri Jan 11, 2019 9:15 pm

Oh, I'm definitely going to have a rubrail. I meant I was surprised to see the EXTERIOR rub rail glued on, which I have always understood to be bad practice. More familiar to me is an INTERNAL rail/gunwale bonded to side-to-deck joint, and then an external rub rail screwed and bedded so that it can be easily replaced if damaged. (And for a belt and suspenders approach, a strip of hollow back stainless screwed over top of the wooden rub rail, which is especially durable!)

My urgent concern, though, is the runners. There is NO mention of them anywhere in the plans except the picture (I searched the digital file and "runners" shows up exactly one place, in the note in the picture I posted.) That picture is relatively small on a much larger, busily illustrated sheet, and not referenced at all in the footnotes that itemize other details on that plan sheet. At 2" x 2" they're also a little beefier than typical runners I've seen, suggesting they MAY be structural. Since there are floor stringers/beams on the INTERIOR in the same location, it doesn't seem likely to me they're needed. But then why is the picture there? And why not marked as "optional" or "recommended" or "required" as other elements in the plans? And why not basic dimensions to indicate their length, where they begin (aft of the bow), etc.?

I suspect they're optional, but before I make an assumption and a potentially costly mistake, I'd like to know the designer's intent/advice.
Wes
---------------------------------------------------------------------------------------------------------
My build thread is here --> viewtopic.php?f=12&t=63644

User avatar
BB Sig
Very Active Poster
Very Active Poster
Posts: 666
Joined: Thu Sep 29, 2011 9:20 am
Location: Monticello, FL
Contact:

Re: Preparing for GT27 build - questions

Post by BB Sig » Fri Jan 11, 2019 9:26 pm

I just looked at the GT23 plans and they are labeled optional. No mention other than showing them under the frames with 1x1 or 2x2 and being optional.

My question to you would be what HP are you installing? Are you going fast around turns that you need to reduce sliding through the turns? If so, go with 2" and go 3/4's the length of the planing surface. If not high HP, go slick!

These runners are not structural!

fallguy1000
Very Active Poster
Very Active Poster
Posts: 2607
Joined: Tue Jan 12, 2010 12:25 am

Re: Preparing for GT27 build - questions

Post by fallguy1000 » Fri Jan 11, 2019 10:15 pm

BB Sig wrote:
Fri Jan 11, 2019 9:26 pm
I just looked at the GT23 plans and they are labeled optional. No mention other than showing them under the frames with 1x1 or 2x2 and being optional.

My question to you would be what HP are you installing? Are you going fast around turns that you need to reduce sliding through the turns? If so, go with 2" and go 3/4's the length of the planing surface. If not high HP, go slick!

These runners are not structural!
Good point, higher hp more need.

More beaching; more need.

Despite being a very different boat; my boat has optional beaching keels. Different name, similar function.

I would size them at nominal lumber dimensions for simplicity.

3/4" or 1.5" or 2.25" square

Recommend ash or white oak. I would make them sacrificial and add them after the bottom work is done. Apply them with 4200 or 5200. Maybe use some ratchet straps. Others will want them mounted more permanently. 5200 is very permanent.. My boat has sacrificial wood strips on top the beaching keels. I plan to epoxy paint them white and same method.

Just trying to help.
My boat build is here -------->

viewtopic.php?f=12&t=62495

wkisting
Frequent Poster
Frequent Poster
Posts: 127
Joined: Tue Jul 10, 2018 11:24 am
Location: Augusta, GA

Re: Preparing for GT27 build - questions

Post by wkisting » Fri Jan 11, 2019 11:49 pm

Yes, but if I proceed as planned with the bottom treatment, attaching the runners later to an epoxy-graphite bottom sounds like trouble to me, especially if the graphite is as slippery as everyone has been saying. I'm thinking my best bet is to err on the side of caution, hold off on bottom coating, spend time to source wood, fashion and bond the runners, re-prep the bottom for graphite, and eat another 1- to 2-week delay from yet another lack of basic detail in plans. Sigh.

Ash or white oak is tricky to source around here unless I go through a flooring store and wait longer than usual for them to get me a special order. It took over a month to get mahogany for the last sailboat I built. More expedient would be to do pine runners capped with 1/8" thick strips of stainless running the full length. Pine is light and stainless is durable. Of course, I still have no idea if these are full-length runners, 3/4 length, or something else...
Wes
---------------------------------------------------------------------------------------------------------
My build thread is here --> viewtopic.php?f=12&t=63644

User avatar
BB Sig
Very Active Poster
Very Active Poster
Posts: 666
Joined: Thu Sep 29, 2011 9:20 am
Location: Monticello, FL
Contact:

Re: Preparing for GT27 build - questions

Post by BB Sig » Sat Jan 12, 2019 8:07 am

The runners are only there for planing and tracking. That's why I asked about the speed. If you are planning for displacement speeds, the runners may not be needed. If you are planning on high speed (over 50 hp motor), then 3/4's of the length of the hull that will be in the water at planing speeds.

ETA:

I just went and measure my "keel" on the GT23. It is less than 7'! I bought it part way through the build and an engineer over thought a lot of things in this boat. I believe he got with Jacques about the length when he got to that part.

Quote from previous builder's blog:
As I took the pictures of our paint job from the front, Greg asked me to post a shot of the skeg, so here it is. The skeg is constructed from a 2X2 strip of cypress (used for its highly water-resistant properties), with a strip of aluminum screwed into the top, after shaping the wood.
YMMV!
Last edited by BB Sig on Sat Jan 12, 2019 8:22 am, edited 1 time in total.

fallguy1000
Very Active Poster
Very Active Poster
Posts: 2607
Joined: Tue Jan 12, 2010 12:25 am

Re: Preparing for GT27 build - questions

Post by fallguy1000 » Sat Jan 12, 2019 8:14 am

Try to not blame JM my friend. They are shown on the drawing. Some people study drawings more thoroughly before they begin the build. In my case, the drawings flowed just ahead of the work; a different drama.

You run a runner the length of expected contact with the bottom. For that boat you could go full length or stop short of the back which might not be great if you beach shallow or with any tidal influence.

5200 will stick to graphite. It can only be cut off.

The trouble with graphite on the runners is it will wear rapidly due to surface area. You can certainly do it, but it won't last long.
My boat build is here -------->

viewtopic.php?f=12&t=62495

Post Reply

Who is online

Users browsing this forum: No registered users and 2 guests