Transom Pods - Flotation and Extended Planing Surface

Use a level and see if the aft cockpit sits level..

 

Another factoid since we have been talking about weight. . . . The propulsion packages (Mercruiser 6.2L Seacore/Bravo 3) weigh 1,244 lbs each, so 2,488 lbs of engine.

IIRC, the 7.4 L engines that I had in my other boat were about the same. The boat itself was a lot lighter.

 

Well. . . the boat properly sits slightly bow 'up', like most boats of this type so that water flows to the stern. Not sure of the inclination angle though.

 

Of course, silly me, if level at rest when she planed out it'd be not..I ought to have a coffee in the morning before I write nonsense...need one now, in fact

 

Looking at the photo of the boat at rest, and the lines drawing it looks to me like it will immerse the underside of the swim platform when transitioning onto plane. This could be significant because the various structures aft of the true transom look like they form an inverted staircase that looks ripe for establishing an unwanted coanda effect with the flow exiting the transom creating significant unwanted hull squat, exacerbating an already stern heavy design. Long trim tabs might be able to cut off this coanda, as might full width interceptors.
Long trim tabs are effectively what you suggest with your buoyancy tanks, but moveable trim tabs or interceptors are more effective than the relatively insignificant volume of buoyancy your tanks/ transom extensions would introduce.

There is also Hull Vane BV, which although it's makers ( Van Oosanen) do not publicly admit as much, is to some extent, a rectification add-on for vessels that through other design compromises or shortcomings are too stern heavy.

 

Very interesting. I’d never seen the Hull Vane system. This looks like it could have been a solution for my 36’ Tiara Open which always felt like a tail dragger.

 

Quick Update . . .

It's been a while. I have the boat out of the water for the season. After a bit more measurement, I am thinking that the swim ladders on either side of the swim platform don't allow for much size and surface area of the transom pods. So, I am re-thinking the design a bit and may go with a swim platform extension and move the swim ladders to it. That change will allow the transom pods to be their intended size/shape/ etc.

Stay tuned for design updates.

 

Re KapnD's photo - brilliant! Improvisation at it's finest.

 

Quick Update . . . Jan 2024

It has been a while and having come to the conclusion that the current position of the boarding ladders would result in the transom 'pods' needing to be too small in order the provide clearance for the ladders. . . . I have designed an extended swim platform for the project, so the 2 boarding ladders will be moved to the extended platform, allowing the T-Pods to be bigger.

Additionally, I will be re-engineering the battery banks and some other things to reduce the overall weight of the boat by about 400 lbs. so the project is now 3-fold . . .

• Battery Banks
• Extended Swim Platform
• Transom Pods

Here are some sketches of the deck layout and the running surface with this approach. The swim platform is fairly simple as compared to the one I made for my previous boat, so it should not add too much work. The boat manufacturer offers a fairly large extended platform as an option, but I'm planning on making one that is a bit smaller, which I think will look better.

Current (standard) Deck Layout


Swim Platform Layout ( Pods are in Red . . . Extended platform in light blue)

Without coloring . . . Ladders will be hidden under the 2 hatches of the extended platform, similar to the OEM ladder design.


Approximate Running Surface

 

Quick Update . . .

I have not been able to make any progress on the swim platform or the transom pods. I may be able to make a few templates from the transom before the boat goes into the water for the season. However . . .

I have reduced some weight of the boat by doing an LiFePO4 battery conversion.

I took out the (7) 31M-AGM batteries (weighing 72 lbs. each) and replaced them with (2) 27M standard (starter) batteries and (2) 100 Ah LiFePO4 batteries. Total weight savings is about 350 lbs.

Batteries removed:

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Electronics board that I made for managing the LiFePO4 batteries . . . This is a work-in-progress photo . . . a few finishing touches remained.

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Here are the batteries, getting them arranged on the now spacious battery shelf. I subsequently installed the battery boxes, which I re-purposed from the original installation. I also re-used/re-purposed the heavy 2/0 cable, since there was lots of it.

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The newly designed electrical system isolates the lead-acid from the LiFePO batteries and has 3 sources of charging for both (Solar, Engine/alternator, Shore power).

The LFP batteries weight about 25 lbs and the smaller lead-acid batteries are 50 lbs each. The LFP batteries run all the accessory stuff, and the 2 batteries deliver similar power to the previous 5 batteries that were dedicated to the accessory power.

 

I'm sure you'll notice the difference in and performance and save in weight

 

If you make the pods; make them from marine plywood. Be much easier to test/attach/remove. Fab is simpler. With your talent; modifying them later to glass/foam will be easy..

 

Summer 2024 Update. . .

The weight reduction from the battery upgrade has resulted in a noticeable improvement in fuel usage. MPG is up about 12% from the original.

As for the transom pods, I have decided to take a different approach and do more of a hull extension and convert the boat to twin outboards. Not an easy project, and I am weighing the options of just selling and buying a same/similar boat with outboard engines, but the price jump is about 2X of what a conversion may cost.

Anyway . . . depending on how this plays out, I'll start a new thread.

 

Makes sense to me, enjoy your boating, and avoid all the work!