Pod/Extension engineering.

[Connor Ferguson]

I have a 23 foot aluminum pilot house, it has a 300 Verado on the back and sits super stern heavy in the water. The boat also has sponsons on the back half of the hull, and the gas tank is right at the stern, making the boat very stern heavy. It has 2 flotation pods full of foam so I’m assuming they aren’t helping. When not moving the boat sits so stern low that the scuppers are under water, it almost looks like it’s taking on water. While up on plane it’s dragging the back end of the boat, the flotation pods aren’t even out of the water. The boat was designed for light 2-strokes of the 80s.

This fall I’m going to do a new pod or hull extension. It’s an expensive job but if it makes the boat run faster and more efficient then it’ll be worth it. However, I only want to do this once, no half butt jobs. Does anyone know of a naval architect that has experience with smaller crafts, or an engineer that would know what needs to be done. I know there are a lot of guys around that make great pods, I want to make sure it’s engineered to work with my boat. Any suggestions are much appreciated.

 

[Tightlines22]

I’ve seen a lot worse. Are the flotation pods dry? Do you have access holes to have a look? Any chance you could shift existing weight forward before you modify things more? Could your fuel tanks be moved forward at all?

 

[Connor Ferguson]

I’ve seen a lot worse. Are the flotation pods dry? Do you have access holes to have a look? Any chance you could shift existing weight forward before you modify things more? Could your fuel tanks be moved forward at all?

The pods are full of flotation foam. Through the drains plugs it looks like it’s waterlogged. There isn’t anything I can move forward. The fuel tank has to stay where it is. There isn’t room under the floor further forward.

That 300 is only pushing me about 20 knots, unless I have throttle all the way down.

 

[cracked_ribs]

I would approach the guys at boat design.net for advice if you want to get into the technical design aspects but honestly this is not overly complex.

You can't move a ton of weight around so the only big design issue is going to be working out the changes in lcg by adding displacement volume.

To me this is more of a practical matter than naval architecture. First you need to cut into those flotation pods and see what kind of weight they're holding because that will substantially impact the effect of replacement.

It's also worth getting a look at the sections of transom they've been covering up because if they're full of salt-saturated foam there could be corrosion to worry about.

If it were my boat, I'd cut into the tops of the pods close to the transom, fit Armstrong hatches as large as I could get, cut out the foam and put it in garbage bags and weigh them, and refloat the boat.

You should be able to work out pretty quickly how much displacement you need to come up to where you want to sit. After that it's just taking it to an experienced pod builder.

Good luck and keep us posted.

 

[Connor Ferguson]

I would approach the guys at boat design.net for advice if you want to get into the technical design aspects but honestly this is not overly complex.

You can't move a ton of weight around so the only big design issue is going to be working out the changes in lcg by adding displacement volume.

To me this is more of a practical matter than naval architecture. First you need to cut into those flotation pods and see what kind of weight they're holding because that will substantially impact the effect of replacement.

It's also worth getting a look at the sections of transom they've been covering up because if they're full of salt-saturated foam there could be corrosion to worry about.

If it were my boat, I'd cut into the tops of the pods close to the transom, fit Armstrong hatches as large as I could get, cut out the foam and put it in garbage bags and weigh them, and refloat the boat.

You should be able to work out pretty quickly how much displacement you need to come up to where you want to sit. After that it's just taking it to an experienced pod builder.

Good luck and keep us posted.

I’ll take a look at boatdesign.net. I just want to make sure the floatation I do add won’t create more problems. 1 person I’ve talked to suggested an extension of the plaining hull. Which would be cutting everything off from the transom back and putting on a new pod that is an extension of the hulls structure, so same lines and everything. No tapering or anything like that. Seems like the simplest solution. Just want to explore all options and learn as much as I can before dropping that kind of $$$.

 

[ericl]

Do you have trim tabs? The should be as large as possible.

Is the engine mounted too low? Cavitation plate must be higher than the bottom of the hull.

Find a way to balance the boat at a single point in the fore - aft plane. Most boat's center of gravity fore - aft should be around 1/3 the hull length from the stern.

If your boat is close to OEM spec's as far as the bracket, recommended engine weight/HP AND the above conditions are not as specified, then I'd say the mfgr mucked it up.

There is also a formula of how far the bracket extends from the stern based on hull length, but I do not recall it.

From the pic's the bracket looks to be of questionable design, and 300 HP plus kicker seems to be way too much weight for that boat.

 

[Connor Ferguson]

Do you have trim tabs? The should be as large as possible.

Is the engine mounted too low? Cavitation plate must be higher than the bottom of the hull.

Find a way to balance the boat at a single point in the fore - aft plane. Most boat's center of gravity fore - aft should be around 1/3 the hull length from the stern.

If your boat is close to OEM spec's as far as the bracket, recommended engine weight/HP AND the above conditions are not as specified, then I'd say the mfgr mucked it up.

There is also a formula of how far the bracket extends from the stern based on hull length, but I do not recall it.

From the pic's the bracket looks to be of questionable design, and 300 HP plus kicker seems to be way too much weight for that boat.

Thanks for the reply. This Boat has had a few changes done to it, like the addition of sponsons, making the boat a double hull from transom to about 2/3 of the way to the bow. It’s had flotation pods added and a beefed up engine bracket. Basically it’s a Frankenstein back there. Another reason I want to cut it off and make it one pod/bracket to balance the boat properly and erase the weird work that the previous owner did. So as far as OEM specs, who knows what they are. The aluminum on this boat is much thicker then a typical aluminum. Making it that much heavier back there. There is far too much metal behind the transom.

 

[casper5280]

This is the type of Pod you need. Full extension from the bottom of the hull not the whole back transom.

 

[Reel Gone]

The pods are full of flotation foam. Through the drains plugs it looks like it’s waterlogged.

That 300 is only pushing me about 20 knots, unless I have throttle all the way down.[/QUOTE]

I would be cutting those pods open and see just what’s going on in there, if they are waterlogged then that is the first thing that needs to be rectified as it would add sooooo much weight to the stern.
Find the real problem before you start dumping money into it , as already mentioned there could be some corrosion issues that may need to be addressed.

 

[Connor Ferguson]

This is the type of Pod you need. Full extension from the bottom of the hull not the whole back transom. View attachment 46393 View attachment 46394 View attachment 46395

Hey Casper, thanks for the reply. Why would you suggest that type? Wouldn’t that not provide as much floatation?

 

[uclueletcharters]

Probably full floater pod that acts as a hull extension. The Vrod is a heavy motor plus they mount further back than yam or suzi. I’ve run euro transom boats so hull all the way back and factory poded boats Grady and Robalo. Was never happy with how my poded boats performed compared to my transom mount engine hulls. Poded boats didn’t hold a low speed plane as well, at various speeds threw weird engine spray. When you come off plane with a poded boat the following wash was big and sometimes would splash quite high up cowling. If you read why Grady switched the 272 to the 282 full hull at rear vs stepped hull like a pod the ride and overall performance is much better with full running surface plus that extra surface will support your power beautifuly at rest

Love the gulfstream wish they would lengthen hull make it euro transom becoming a 252 from a 232

 

[Rockfish]

I am curious about the decision to put open cell foam in a pod since it acts like a big sponge. The foam would also make inspection of the inside of the pod impossible. My pod is a large hull extension flotation type that only has air in it and some lead ballast. The main motor is an Opti and since big six cylinder two strokes weigh significantly less than the equivalent 4 strokes, the ballast can be removed or decreased to compensate if you change to heavier motors or motor/ kicker combination. I use to be nervous as to what would happen if the pod were to ever be flooded until it actually happened. I had pulled the inspection hatch to check out the inside condition once and apparently not got it properly resealed; normally it is air tight. Water washing over the low pod deck got into the pod to the point the stern dropped and the inspection port was an inch below the water line and the pod was full before we noticed it. There was no pumping it out at sea from the top. We were trolling at the time.
This did change the balance of the boat and limited our top speed even with the available trim range to push the bow down and transferring extra weight to the bow, but still managed about 15 to 20 mph back to the marina, where we pulled the boat out and removed the drain plug and resealed the inspection port seal, correctly this time. That was the only time we have ever had a problem with it.

 

[tyeeking]

I would absolutely remove the waterlogged foam before doing anything else. You are likely holding a huge amount of weight in that foam not to mention all of the other problems that come with lots of water on the wrong side of the hull. You might surprise yourself with how much that improves how your boat sits in the water.

 

[fishin solo]

Hey Casper, thanks for the reply. Why would you suggest that type? Wouldn’t that not provide as much floatation?[/QUOTE
That will be plenty...... and you won’t have to worry about porpoising or anything.

 

[uclueletcharters]

It’s my understanding new foam is pretty water resistant. I do know of a fella that had no foam but he had an auto bilge pump in pod that worked well

 

[Rockfish]

It’s my understanding new foam is pretty water resistant. I do know of a fella that had no foam but he had an auto bilge pump in pod that worked well

I had thought about the pump idea but decided against it. I am curious where he put the outlet since these type of pods have almost no free board, I wonder about water getting into the pod through the outlet. Some sort of one way valve or perhaps a welded Al tube curved over at the top, rising up out of the pod deck which could be rather vulnerable to damage. There would also be a need for a small port/additional hole in the pod for the wiring and the access port distance for servicing to the pump and hose connectors etc could be a problem on our boat as it is rather deep although we can get the lead ballast out through the inspection port if we have to. I am thinking that the less holes in the pod to fail or cause problems the better.

A water level alarm sensor would be easier to let you know that you have lost pod integrity and water is getting in but one would still need the electrical port and some sealed in moisture in the pod does occur from condensation and residual from being drained etc. The pod system on our boat has been problem free for close to 15 years other than the issue with not being careful the one time on the inspection access port resealing. Even with complete pod water intrusion failure in our case it does not sink the boat and you can still make good headway although the boat would have somewhat reduced seaworthiness which could be an issue in heavy seas.

 

[casper5280]

No foam as Tyeeking suggested it just holds water and in a aluminum pod that is no good. Also get a very good inspection port, drain plug and make sure both are sealed well, that is the key to a good pod build.

 

[uclueletcharters]

You could use a through hull on pod to transom come out top then tube to your next through hull through transom to run wires and bilge pump tube. You could also when on trailer fill pod full of water and even put some dye could be cool aid and look for leaks on outside.

 

[beemer]

get rid of the foam and play with props and engine height. The boat seems to plane nicely judging by the photos. Pod may not solve your problems. I would spend my money on moving the fuel tank forward.

beemer