Author Topic: extended swim platform  (Read 183 times)

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Howie

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extended swim platform
« on: November 03, 2024, 08:40:55 AM »
Hi All-

Mulling over ideas for a rear transom/swim platform. I thought this was interesting idea from Ranger. Have not really seen much feedback on it but thought I would throw it out there to get some thoughts on it. It is basically "wings" that extend the swim platform past the end of the OB.

https://www.rangertugs.com/ownership-experience/blog/content-container/what-is-the-clear-path-swim-platform/

My thoughts:

I like the idea of a really easy way to board from either side of the boat on the platform. I am going to have a single transom door to stbd and I do plan on some sort of canvas cockpit enclosure...having an easy way to get across behind the OB would be great. Even if I did a "standard" euro transom, I like the idea of routing the motor cables and lines down and under the swim deck as opposed to directly into the false transom. Less to trip on, etc.

Their implementation seems to preclude the ability to add a kicker. I guess if you had the kicker really close to the main you could shrink the "wings" but on a 8'6" beam boat, I don't know how much would be left to be useful on the kicker side. The kicker could be mounted to the end of a wing, but that is getting pretty far out there even though a kicker is relatively lightweight.

While our boat will hopefully have gobs of solar I am looking at the possibility of having a portable generator to run some sort of A/C if we eventually do some boating in the Southeast. (I'm originally from Georgia and escaped the humidity for the PNW, fortunately). The generator and A/C would most likely a temporary/removable thing for specific trips. The "wings" seem like a great spot to strap down a small honda gen to get the noise and exhaust away from the cockpit (yes, I know portable gens on a boat is a big debate). Could also be used to store crab pots out of the way maybe?

Seems like it could complicate trim tabs and any transom mounted transducers.

As they have this, the wings look like sponsons but they don't have any flotation. Would adding flotation to these help a GA designed on the heavier side?

I guess the simplest implementation of this would be adding a couple of bolt on swim platforms on either side of a euro transom. Seems like that is asking to get whacked during docking operations though. Maybe something that folds up?

Curious what other folks think.
 
« Last Edit: November 03, 2024, 08:42:59 AM by Howie »

Dan Boccia

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Re: extended swim platform
« Reply #1 on: November 03, 2024, 01:56:03 PM »
You can see on my build thread I went with a standard transom, with after-market swim step/ladder on port side, and kicker bracket/kicker on SB side. I really like my setup. I'm not a fan of full-width swim steps, as I prefer more useful space on the back deck/cockpit, and the lockers on either side of the engine well for batteries and electrical gear. I like what Ranger has done, and you could certainly make the side with the kicker only extend out far enough to allow for the kicker to trim up out of the water all the way.....but then again that could just be done with a simpler kicker bracket. Lots of pluses/minuses and compromises that only you can make the ultimate decision on.

Regarding a generator and AirCon, I always advise on these boats to try to avoid 120V AC electrical unless you really want/need it. AC adds significant safety hazards, maintenance, cost, corrosion potential, and weight and very few owner-builders are prepared to figure out the code/safety issues for these systems. If you do go AC, the next step is to try to avoid having a shore power system, which is #1 culprit in boat fires. And finally, if you decide to go with AC and shorepower, do yourself a favor and really design a proper locker/layout for it, and go with SmartPlug connections for sure. The ELCI, inverter/charger, AC panel, galvanic isolator, enlarged house battery bank etc. take considerable space to layout properly. Enjoy scheming and designing!

Brian.Dixon

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Re: extended swim platform
« Reply #2 on: November 04, 2024, 07:32:00 AM »

Well thought out!  I like that!  IMHO, there's nothing wrong with a 'wing type' (as you call it) swim step/platform on one side.  I'd go with a thru-hull transponder or put your transom type under the swim platform side ... kicker on the other.  As far as weight and balance go, keeping in mind that 2/3rds of a planing hull is forward of the CG, you should take into careful consideration all that goes f'w'd.  If you are going to highly-outfit the boat for almost live-aboard accommodations, then it may mean a disproportionate amount of weight ending up f'w'd of the CG as mentioned.  Using those 'wing type' swim platforms and the main on a bracket to move it aft, then that's an opportunity to help move the CG aft if your accommodations are moving it f'w'd.  This is true more so for the Kodiak, which was designed for 'commercial or serious recreational fishing" ... in other words, more stern weight capacity. 

A good way to estimate your CG location is to look at the 000x series of drawings that come in the plans and study the construction details very carefully ... if you build the boat exactly as shown in those drawings, it will trim 2-1/2" up at the bow.  Whenever you add something heavy f'w'd of the CG that is in excess of what you see in the 000x drawings, then figure out a way to counteract it with weight of some sort behind the CG ... compare moment-arms.  Here's an example:

Consider a boat that's exactly like the one in the 000x drawings and add a 70# anchor winch and 50# bow-thruster to the bow (about 19' forward of the CG more or less).  The newly-added forward moment-arm of those items is 19' times 120#, about 2280 ft-lbs.  To counteract that, move the 100# of batteries that are right behind the aft house bulkhead aft to the transom and put the main motor on an 8" bracket (0.66 feet).  Assume the bracket weighs 40# and the motor weighs 500#.  Complex, but here goes. Removing the batteries from the house bulkhead reduces the forward moment-arm by approximately 3 feet (they were ahead of the CG by 3 feet) times 100#, about 300 ft-lbs.  This reduces the bow-down moment of the battery's original location by 300 ft-lbs.  Adding the batteries to the transom (inside the transom about 8' behind the CG) creates an additional bow-up moment-arm of 800 ft-lbs.  The net result of the battery move is an 1100 ft-lb bow-up moment change.  Now for motor and bracket.  Bracket is about 9' behind the CG and weighs 40#, a 360 ft-lb bow-up moment.  The motor's original moment-arm is 9' times 500#, or about a 4500# bow-up moment-arm.  Moving it to 9.66 feet further aft gives it a 4830 ft-lb moment for a net increase in a bow-up moment of 330 ft-lb.  The net trim change in bow-up moment is:

-2280 (anchor winch and bow-thruster) + 1100 (battery move) + 360 (added motor bracket) + 330 (motor move), or about a net -490 ft-lb bow-down trim.  Considering the boat likely weighs 5000+ lbs on the water, this likely won't cause a large bow-down trim.  Perhaps the original 2-1/2" bow-up trim becomes a 1" or 1-1/2" bow-up trim?  That would be fine.  But NOTE that if you used a 100# bow-thruster and a 150# big commercial anchor winch, their bow-down trim would become 4750 ft-lbs ... an increase in bow-down trim of 2470 ft-lbs ... a ton and a half!  THIS is why you really want to pay attention to WHERE extra weight is added and how well you've balanced it out.  Seemingly small decisions can make big differences.  This is because the GA is light for it's size ... making the boat half as expensive to build compared to one that weighs as much as a commercially-manufactured vessel, and giving you double the gas mileage so your boat can have an extended range and reduced cost of operation.  It's a fair trade.  A commercial 10k lb boat would not notice changes in the locations of items that a 5k lb GA would.

I retire as of March 1 ... high on my list is the creation of models and spreadsheets that will allow me to help builders dial-in their boat's layout in a most optimal way.  Also on the list is a fine tuning of the Standard and Kodiak GA's, now that they've been on the water for a long time and we can see what the typical usage is, designs around a slightly different weight arrangement.  NOTE that this will be a MINOR improvement in the designs ... the main issue in terms of trim is the boat's light weight combined with the fact that planing hulls have 2/3rds of their weight forward of the required CG envelope.  This is why live-aboard boats are DISPLACEMENT hulls rather than PLANING hulls ... a boat that's required to plane requires careful considerations and is by default more sensitive to things like weight distribution.  There are some beautiful live-aboard type accommodations in several GA's out there that demonstrate that it's possible.  You just have to pay attention and tune as you go.  Note that the Kodiak addendum document lists several ways to move the CG around should you need to.


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Howie

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Re: extended swim platform
« Reply #3 on: November 04, 2024, 08:55:46 AM »
Thanks for the detailed reply!

I have done a bit of this type of CG balancing act on a small camping trailer I have spent some time designing, mostly to calculate tongue weight. I created a spreadsheet to do the calcs and help wrap my head around what was happening. I still get surprised at how much difference a small weight can make far out. Levers, right?

Congrats on the upcoming retirement! I had seen some posts from you mentioning a minor update/clarification for more camping focused boats and was going to ask you about that...glad that is still in the works. 

I think a spreadsheet would be a big help for folks planning something like this. I wonder if it would be helpful to also provide a "bare boat" baseline GG and bow trim. Say with just the PH exterior and no tanks, batteries etc. Then if someone had the patience they could really dial in the weight of things they are adding to the boat.

Clearly from the successes posted here you can have it all with a GA...speed, utility and comfort (within reason). Appreciate you getting into the details on this. It is great that your design has so much latitude for folks to make them what they want.

Brian.Dixon

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Re: extended swim platform
« Reply #4 on: November 04, 2024, 02:59:20 PM »
Howie ... When do you think you'll start building?
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Djeffrey

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Re: extended swim platform
« Reply #5 on: November 08, 2024, 12:50:59 PM »
I love your idea. I also extended and put in a tuna door. Makes getting on the boat easy, from the dock or out of water

Howie

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Re: extended swim platform
« Reply #6 on: November 08, 2024, 02:19:58 PM »
I love your idea. I also extended and put in a tuna door. Makes getting on the boat easy, from the dock or out of water

Hi! Your boat looks great and is very much along the lines of what we want to do. I have scrolled through your build many times. I really like curved transom. Do you think it would work to make the whole deck at the level of the center section? Not sure if that would start to affect the usability of things. Anything you would have done differently?

I did end up finding a video of someone who has a ranger with that extended deck. The grab bar and swim ladder storage is interesting too. I saved a "clip" of it so you don't have to watch the whole video to find it:

https://www.youtube.com/clip/Ugkxn3So5pdyShpkM_Z2lAZrI_J0UESQugma


Brian.Dixon

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Re: extended swim platform
« Reply #7 on: November 08, 2024, 04:25:48 PM »
The curved transom is a VERY good idea and much stronger than a regular flat transom ... but the flat transom is well-supported inside the boat.  The entire boat was designed overly-strong by a high percentage, the idea that you could build it out of any cheap exterior BCX plywood out there and be fine.  But I do like that curved transom.  if the motor had been hung right on it (or a bracket right on it), the curve of the transom would prevent transom flex as the motor kicks up and down, on water or on a trailer.

You can make the swim platform the same height clear across, no problem.  I also love how this pic shows how hugely the swim platform w/door enables getting in and out of the boat.  Important for toddlers and/or people who aren't entirely stable on their feet ... and you don't have to climb past fishing rods, downriggers, or crab davits either. 

I do prefer a door that swings outward though (hinges on the side closer to the motor) so that stern seas hitting the transom compress the door against seals rather than trying to open the door.  I plan on adding the euro-transom and swim platform to the plans when I update them next Spring... and a few other tune-ups such as giving the cockpit deck a good downward slope to the transom to help keep the boat self-bailing even if you have two people the size of me sleeping in the bow overnight during an extended rainy period.

Brian

« Last Edit: November 08, 2024, 04:29:06 PM by Brian.Dixon »
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Djeffrey

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Re: extended swim platform
« Reply #8 on: November 08, 2024, 05:48:21 PM »
Only thing I would have done different is to slope the back deck to the rear 1 to maybe 1 1/2 inches. I enjoy this boat so much. Have thought about building a new one but don?t want to get off the water to do it. Just been upgrading a few things so I can spend more time on it.

Brian.Dixon

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Re: extended swim platform
« Reply #9 on: November 09, 2024, 07:16:37 AM »
Only thing I would have done different is to slope the back deck to the rear 1 to maybe 1 1/2 inches. I enjoy this boat so much. Have thought about building a new one but don?t want to get off the water to do it. Just been upgrading a few things so I can spend more time on it.

Yeah .. that's one of the updates that I plan for the manual(s) when I give them a refresh this Spring (after I retire, 3/1/2025) .. make it standard practice to raise and slope the cockpit deck, e.g. raise the deck 1-1/2" at the transom and around 4" at the aft house bulkhead.  Also standard practice is that every under-deck bulkhead gets a pluggable (15/16" diameter) drain hole ... clear into the cuddy.  Plug all when underway or sleeping overnight, but open all when trailering (and at a dock IF you are SURE the boat is trimming bow UP).  Finally, if you plug all but the aft cuddy bulkhead drains, then the deck inside the house is high enough to put a bilge pump just aft of the aft cuddy bulkhead, e.g. on the house side of the bulkhead.  If you sleep in the bow and have gear forward, you want the cuddy deck to be self-bailing, and have the cuddy bulkhead bilge pump as a back-up.  Note that if underway and you do have water under the deck, that you can flush most of it just by opening all plugs and getting on plane for a few moments, then plug all bulkheads again before coming off plane... old trick for people that own planing hulls.

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