Author Topic: Closed transome  (Read 5185 times)

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jadranko

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Closed transome
« on: February 07, 2010, 03:13:24 PM »
I have been looking for right project for about 2-3 years and I think I found it.

Right now I have question about closed transome, is it possible ? ( I want to have more space at aft )

I would like to have outboards setup like this :

- 3 outboards on Porta bracket ( hydraulic bracket which can lift up and down outboards ) with set back of 26", how will this affect to CG ?

- two 115 hp 20" Evinrudes on each side and one 25 hp 25" kicker for trolling in the middle (with separate tanks and controls)

And please tell me something about what is predicted behavior Gerat A. at displacement speeds, do you maybe have projection of knots vs hp ?









Brian.Dixon

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Re: Closed transome
« Reply #1 on: February 07, 2010, 04:05:12 PM »
I have been looking for right project for about 2-3 years and I think I found it.

Right now I have question about closed transome, is it possible ? ( I want to have more space at aft )

I would like to have outboards setup like this :

- 3 outboards on Porta bracket ( hydraulic bracket which can lift up and down outboards ) with set back of 26", how will this affect to CG ?

- two 115 hp 20" Evinrudes on each side and one 25 hp 25" kicker for trolling in the middle (with separate tanks and controls)

And please tell me something about what is predicted behavior Gerat A. at displacement speeds, do you maybe have projection of knots vs hp ?

Hi Jadranko,

  I will try to answer your questions one at a time.  Yes, a closed transom is fine (see attached) and the details already completed.  This was for a sterndrive option, but should work for a bracket as you describe.  My only comment on the horsepower choices is that they seem a bit high.  This boat is a lighter than your typical fiberglass or aluminum boat and requires a lot less horsepower (and gets a lot better mileage).  Unless you are really going to load the boat down, 175 hp (total) would be fine.  For twins, you could use twin 90's, or round up to twin 100's or 115's primarily.  The larger options would primarily be for higher speed, possibly planing, if you lost one motor and had to return on one... but you certainly don't need that much horsepower for normal operation.  The same applies to the trolling motor.  A 15-hp trolling motor would work fine, but rounding up to a 25 hp would be OK.  If trolling motors are too big, then you risk not being able to troll slowly enough unless you buy an extra-low pitch and/or smaller diameter prop for it.  Here's a link to the hydrodynamics (displacement and planing, speeds and stability) analysis that I performed on this design:

  http://www.glacierboats.com/node/36

  Note that the analysis above is for a perfectly smooth hull with no parasitic drag, e.g. drag caused by skegs, strakes, trim tabs, motors etcetera ...the predicted speeds are about 10% faster than what you'd realize in the real world.

  As for mounting your motors behind the transom on a 26" porta bracket, it's possible but I'd want to get more information from you on your intended accommodations, fuel requirements, and what not so I could do a careful CG analysis prior to your committing to your plans.  I think that the worst case would be giving up the aft belly tank and moving fuel forward either into saddle tanks under the port and starboard sheer decks or a pair of box tanks hiding in a settee or other location (just inside the aft pilot house bulkhead) to counter the weight of the motors being moved aft.  Your selection of 230 total horsepower leads me to assume that you are leaning towards a 28' (longer rather than shorter) boat?  If so, then it'll be more resilient to shifting CGs than say a 25' Great Alaskan would be.   See Inboard Construction Profile (attached).

Brian


jadranko

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Re: Closed transome
« Reply #2 on: February 07, 2010, 04:44:42 PM »
Thank you for now Brian, I will provide you additional details when I purchase plans.

jadranko

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Re: Closed transome
« Reply #3 on: February 09, 2010, 01:31:38 PM »
I downloaded plans and have a quick look ... is this all sheets ... lets say I have feeling that somethings is missing there.

Brian.Dixon

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Re: Closed transome
« Reply #4 on: February 09, 2010, 03:15:11 PM »
I downloaded plans and have a quick look ... is this all sheets ... lets say I have feeling that somethings is missing there.

No problem.  You will notice that there is a 'brief' construction manual that may be appropriate for those with a reasonably high level of experience, and then the 'regular' construction manuals.  The regular construction manual comes in 2 parts.  The first one includes a lengthy introduction to materials, epoxy, fiberglass, techniques and the step-by-step instructions for building the hull to the point where it is turned upright.  The sheets (drawings) supplement the construction manuals, both so you can visualize the parts you will build and to provide the dimensional information.  The second part of the construction manual begins where the first left off and guides you through the addition of decks and superstructure (pilot house and cuddy), finishing with ...well, finishing (painting etc).

If you do, however, spot something that's missing or confusing, please do let me know.  As far as your order of events go, I would suggest glancing through the drawings to get just a basic familiarity with what is there, then skim through the brief construction manual.  This will give you a high level view of the construction sequence and how things come together.  Then I would just start reading at the beginning of the first manual and go from there.  The manual will tell you which drawings (sheets) to use and when. 

Be sure and continue to post your questions here so that all can share in the both the questions and in the answers or answering of the questions.  Photos are always great too, and I am willing to host blogs or web sites for someone if they want or need a place to document and show their progress.  Check out Adrian Pau's photo gallery in the Projects forum for example.  He's using PhotoBucket for his project.

Thanks,
Brian


jadranko

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Re: Closed transome
« Reply #5 on: February 10, 2010, 07:31:44 AM »
Right, for sure first I will study construction manual, and do some notes, I already started.

And I have first question, what is the height of upright finished boat on cradle ?

I will build low cost shelter, so I must know that.



 

Brian.Dixon

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Re: Closed transome
« Reply #6 on: February 10, 2010, 09:50:13 AM »

...I need to open the CAD project to determine the height of the finished boat on the cradle.  You may want to allow extra height if you can, since you may find yourself putting the boat onto a trailer before it's finished, and then finishing it.  More info tonight...

Brian.Dixon

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Re: Closed transome
« Reply #7 on: February 11, 2010, 01:01:07 AM »
Right, for sure first I will study construction manual, and do some notes, I already started.

And I have first question, what is the height of upright finished boat on cradle ?

I will build low cost shelter, so I must know that.

OK... I opened up the jig and bottom panel molds drawings and the Prince Rupert 3D CAD model and find that the floor to top of pilot house roof distance is a total of 9' 9".  Add 4" or so and you find that you need at least a 10' ceiling and door height to squeak the boat through.  I'd recommend that you go with 11' as a minimum for ceiling height, and 12' or 13' would be even better since it is likely that you'll be on top of the boat yourself as you finish it.  THAT said, note that this assumes that the upright boat is carried upon the original building jig which has a top surface 23" above the shop floor.  Upon turning of the hull, you can of course lower the building jig prior to putting the upright hull on it.  Just pre-build mounts for the casters and put them on while the upright hull sits in the driveway, then put the hull-support molds onto the jig (I can send photos), and bring the boat back in.  This will drop the total height to about 9' or so (plus the curbing/visor around the roof if you're building the Prince Rupert or Newport).  If you go the other direction and put the upright hull onto a trailer right away (usually not suggested), you'll need more door and ceiling clearance.

Hope this helps... but let me know if not or if you need more information.

Brian