# Float pod Trim tabs



## Guest (Aug 14, 2018)

Is there room under the pods to mount them and clearance on the back for the actuators to attach?


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## NCSkiff (Aug 14, 2018)

My plan is to build the pods tall enough for the actuators to mount to, and mount the pods an inch or 2 above the bottom of the boat.


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## Guest (Aug 14, 2018)

I’m gonna say, since they aren’t already installed... mount the pods as close to the bottom of the hull as you possibly can so you recognize the positive flotation from them. Hang the tabs on the back. If you mount them 2” above hull bottom the the boat will have to set down those same 2” before the pods start to work.


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## NCSkiff (Aug 14, 2018)

Would you flush mount them under the pods or sticking off the back of the pods? Trying to avoid the 2nd option because it seems they would get in the way or get broken easily


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## jay.bush1434 (Dec 27, 2014)

To maximize the buoyancy of the pods, mount them flush to the running surface of the hull. For the tabs, just mount on the back of the pods. Makes for easier installation and much easier repair/replacement down the road. My Vantage has big tabs and they don't get in the way. Actually, the motor sticks out farther than the tabs.


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## NCSkiff (Aug 14, 2018)

Will mounting them flush to running surface increase drag while running? Or am I just over thinking it? Do you have a picture of your setup?


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## Guest (Aug 14, 2018)

If you don’t flush mount them, you’ll see very little return from your investment! The tabs are pretty darn tough so mount them on the back and go fishen!


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## NCSkiff (Aug 14, 2018)

Regarding the pods, is it best to have them level with the original running surface, or angled up like ones in link below. Maybe not that aggressive of an angle
https://goo.gl/images/2g3Pxz


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## Guest (Aug 14, 2018)

If level, you might find you don’t need trim tabs. With a slight angle you lesson the chances of affecting ride/ handling by not getting them perfect. I would mount them level and make sure they are installed perfect, then decide if I needed tabs or not. Tell us about your boat/motor package.


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## NCSkiff (Aug 14, 2018)

It is not a micro skiff, but I am applying micro skiff ideas to it per say. It is a 20' cape fisherman semi V. I have added a tunnel and motor will mount on a jack plate probably, 14"offset. I want to add the float pods to make up for the flotation lost with the tunnel, and the offset of the motor


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## jay.bush1434 (Dec 27, 2014)

NCSkiff said:


> Will mounting them flush to running surface increase drag while running? Or am I just over thinking it? Do you have a picture of your setup?


Over thinking it amigo...


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## DuckNut (Apr 3, 2009)

NCSkiff said:


> Regarding the pods, is it best to have them level with the original running surface, or angled up like ones in link below. Maybe not that aggressive of an angle
> https://goo.gl/images/2g3Pxz


Look at the picture you posted. There is very little benefit from the pods as drawn. Make them like Jay's picture - an extension of the hull rather than an addition.


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## NCSkiff (Aug 14, 2018)

The link below Is kind of the shape I had in mind since the deck drains will come out the back also
https://goo.gl/images/H2t5DJ


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## DuckNut (Apr 3, 2009)

There you go...sponsons (extension) rather than float pods (additions).

Now cut the top out and make them livewells.


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## Smackdaddy53 (Dec 31, 2012)

Here’s how I mounted them on a boat I built. Don’t overthink it. They don’t add any drag if mounted as designed because they are at a slight angle up (3/8” if I remember correctly) when in the highest position. This hull ran 33mph loaded down with gear, 18 gallons of gas and two biscuit heads.


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## NCSkiff (Aug 14, 2018)

jay.bush1434 said:


> Over thinking it amigo...
> View attachment 37256


Jay, are the float pods in your picture just as thick as the actual transom where the motor is bolted on, or are they just the fiberglass skin like the hull of the boat?


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## NCSkiff (Aug 14, 2018)

DuckNut said:


> There you go...sponsons (extension) rather than float pods (additions).
> Now cut the top out and make them livewells.


Sorry about the terminology, everyone seems to call them something different and not a whole lot of info on them on google except for pictures. That is a good idea on the live well, but wouldn't that defeat the purpose of adding them for more flotation?


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## Vertigo (Jun 3, 2012)

I question the whole idea of adding a tunnel, 14" setback jack plate, pods and trim tabs to a hull that is a heavy semi-v. If this kind of modification is necessary to get the performance the OP wants, then maybe it's time to consider an entirely different hull. None of these mods is going to make a Cape Fisherman 20 into a flats boat.


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## NCSkiff (Aug 14, 2018)

Vertigo said:


> I question the whole idea of adding a tunnel, 14" setback jack plate, pods and trim tabs to a hull that is a heavy semi-v. If this kind of modification is necessary to get the performance the OP wants, then maybe it's time to consider an entirely different hull. None of these mods is going to make a Cape Fisherman 20 into a flats boat.


 I understand what you are saying, I am trying to see if adding the pods like are on most flats skiffs will help the performance of a heavier boat like mine. I posted in this forum because I figured you guys would have most knowledge of these setups.
There are plenty of boats in my area that have very similar hull designs (sea ox, parker and may craft) that have added tunnels and jack plates and are able to run in 4-6 inches of water, but take around 12 inches to float sitting still. I am throwing around the idea of putting pods on the back to help it float in less water while sitting still, and help the boat plane out better. Below is a boat that May craft is making from the factory with a tunnel.


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## Vertigo (Jun 3, 2012)

Adding a tunnel and jack plate to a Cape Fisherman 20 semi-V will NEVER result in a boat that will run in 4-6" of water. It's a 2000# hull that draws 12" with the motor tilted out of the water. Purposely designed flats boats will have a hard time running that shallow.


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## NCSkiff (Aug 14, 2018)

4-6" is a stretch. I have personally rode on a couple Semi-V boats with tunnels in less than 12". Probably around 6-8" range.


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## Vertigo (Jun 3, 2012)

Let's do some math. 12" draft (unladen), 4" tunnel puts cav plate 8" below water surface. 15" dia prop puts skeg 23" below water surface. Running on plane may raise the stern a few inches, but will never raise the 17" needed to run in 6" of water. 

In the real world, you'll probably need close to 2 1/2 feet of water for a hole shot and run in about 18". I don't mean to rain on your parade, but it's better to have realistic expectations before you spend a lot of time and money on this project.


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## DuckNut (Apr 3, 2009)

NCSkiff said:


> Sorry about the terminology, everyone seems to call them something different and not a whole lot of info on them on google except for pictures. That is a good idea on the live well, but wouldn't that defeat the purpose of adding them for more flotation?


No because the overflow flow hole would be above the waterline. The pods will do what they are designed to do regardless if there is a top or not. Just like pushing an open 5 gallon bucket into the water - it still displaces water without a lid.


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## DuckNut (Apr 3, 2009)

Hydrofoils.............


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## jay.bush1434 (Dec 27, 2014)

NCSkiff said:


> Jay, are the float pods in your picture just as thick as the actual transom where the motor is bolted on, or are they just the fiberglass skin like the hull of the boat?


NCSkiff, they are molded as part of the hull and are "hull thick."
Personally, I think if you pods are done right, along with tabs, and jackplate, you could gain an inch or two in static draft, take off draft and on plane draft. I've also seen those pods done with some aggressive non-skid and they work well for boarding the boat from the water. Even still, I'd be surprised to see anything less than 10" draft. Good luck and keep us posted...


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## bryson (Jun 22, 2015)

I'm interested to see some of the discussion on this topic. I've been thinking about doing something similar to my old lappy -- basically creating a hull extension so that it looks just like it came with sponsons (or a keyslot transom, whatever you want to call it) from the factory, rather than add-ons, just like the photo @jay.bush1434 posted of his Vantage.

The stern is a little heavy with my motor, and I feel like I could get back a few inches of draft, with very few sacrifices I can think of.


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## Smackdaddy53 (Dec 31, 2012)

jay.bush1434 said:


> NCSkiff, they are molded as part of the hull and are "hull thick."
> Personally, I think if you pods are done right, along with tabs, and jackplate, you could gain an inch or two in static draft, take off draft and on plane draft. I've also seen those pods done with some aggressive non-skid and they work well for boarding the boat from the water. Even still, I'd be surprised to see anything less than 10" draft. Good luck and keep us posted...


Pods will never gain a hull 2” less draft unless they are ungodly huge and then you have other issues. The wetted area of a pod is the only displacement they add and that little bit MIGHT net you 1/4-1/2” less draft. A cubic foot of air floats about 62 pounds and it takes a lot of pod under the waterline to get that much displacement. 2” less draft would take a whole lot of added displacement to attain and if you add the weight of a jackplate, pod material and trim tabs you are just about back to the original draft. Been there done that! It’s better than not having the planing adjustments of tabs and ability to raise the motor but as far as floating skinnier it’s probably not happening.
I know a lot of people that think that filling a hull with foam will make their boat float in less water...it’s only true if there is a hole in the hull!


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## bryson (Jun 22, 2015)

Smackdaddy53 said:


> Pods will never gain a hull 2” less draft unless they are ungodly huge and then you have other issues. The wetted area of a pod is the only displacement they add and that little bit MIGHT net you 1/4-1/2” less draft. A cubic foot of air floats about 62 pounds and it takes a lot of pod under the waterline to get that much displacement. 2” less draft would take a whole lot of added displacement to attain and if you add the weight of a jackplate, pod material and trim tabs you are just about back to the original draft. Been there done that! It’s better than not having the planing adjustments of tabs and ability to raise the motor but as far as floating skinnier it’s probably not happening.
> I know a lot of people that think that filling a hull with foam will make their boat float in less water...it’s only true if there is a hole in the hull!


Another big thing is figuring out how much draft is affected by weight. You could add 2 cubic feet beneath the waterline to displace nearly 130 lbs, but you need to know what that means with respect to draft. On a large, heavy boat, that may be an inch or less. On a skiff, it may be 2-3 inches.

You can approximate it by adding the weight to the transom and seeing how it changes. For example, I've seen photos of my boat with a 260# motor on it, and my motor weighs 420#. The difference in draft appears to be about 2 inches. So I know that for my particular boat, 160# of displacement will float me somewhere near 2 inches higher. By the time I factor in the added weight of the sponsons, that's nearly 3 cubic feet of water I need to displace. If I assume a final draft of around 11 inches, my sponsons would need to be over 2' wide and 1' long (if they follow the lines of my hull).

All that being said, you've definitely got the real estate for large pods. Make some that bolt on, and test them out. If you don't like how they work, then you can take them off and you'll be no worse for wear after a little touch-up glass work. If you do like them, then you can refine them or leave them as-is.


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## jay.bush1434 (Dec 27, 2014)

Ok, so I was probably over guessing at 2" of draft but there is a lot of boat underwater already. Depending on where the pods are mounted, both of them could be pretty much awash giving full buoyancy. 1 cubic foot of volume isn't that much for a pod on a boat with that much beam and transom so assuming there is approximately 120lbs of added buoyancy from 2 pods right at the transom where it counts the most. That is about 1/3 of the weight of that outboard or about 16% of the weight of the boat, assuming 2000lbs. I'm no naval architect and I didn't sleep at a Holiday Inn Express last night either so I could be way off. I'm definitely interested in seeing how it comes out.


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## DuckNut (Apr 3, 2009)

Smackdaddy53 said:


> A cubic foot of air floats about 62 pounds


I agree with you smack in this but I think there may be some law of gravity or a dead persons principle at work here.

What I am picturing is a sealed cubic foot square and a 50 pound weight. This is where my question comes in: If I attach the weight to the bottom of this square box how much of the box will rise above the waterline? If I attach it to the top how much of the box will be above the waterline?

Are these the same amount? I am guessing no. I think they would be relatively close but I think the one with the weight under would be a bit higher out of the water. I get this rationale because whatever I am "lifting" will weigh less under water than it does above water. This is the principle of how things float.

I could be wrong in my thinking.

In order to run shallower lift has to be created. If the boat has a tunnel, this will created lift more than the V. Adding lifting strakes will also help to a degree. A running pad will help. All of this will only do so much to get the boat up in the water before another force has to take over. The second force is air lift.

An Allison bass boat goes what - 100mph and nearly nothing in the water but prop. This tells me that there is more at work here than simply displacement. Certainly the boat is not floating on the last 1 foot of hull. Sumtin' more is happening.


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## bryson (Jun 22, 2015)

DuckNut said:


> I agree with you smack in this but I think there may be some law of gravity or a dead persons principle at work here.
> 
> What I am picturing is a sealed cubic foot square and a 50 pound weight. This is where my question comes in: If I attach the weight to the bottom of this square box how much of the box will rise above the waterline? If I attach it to the top how much of the box will be above the waterline?
> 
> Are these the same amount? I am guessing no. I think they would be relatively close but I think the one with the weight under would be a bit higher out of the water. I get this rationale because whatever I am "lifting" will weigh less under water than it does above water. This is the principle of how things float.


This is kind of fun to think about -- let's say the box weighs 5 lbs, and let's imagine the 50 lb weight is a 1 square foot plate, mounted to one side of the box.

So, no matter how the weight is mounted, the whole assembly will displace 55 lbs of water. If the extra weight is on the bottom (the plate is underwater), it's volume will contribute to the buoyancy, so more of the actual box will be out of the water, but the draft will be the same. If it is on top, only the submerged part of the box is creating the buoyancy, so less of the actual box is out of the water. Either way though, the same *volume* has to be underwater, since that's what drives the amount of buoyancy.

If the weight were shaped differently (say, a 6 inch cube, or really any shape where the cross-sectional area is less than 1 square foot as it protrudes from the box), then the draft would increase when it's on the bottom.

I don't know how much all that applies to designing float pods, though. Also, all this is just static draft. The pods adding lift or increasing the planing surface is a totally different ball game.


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## DuckNut (Apr 3, 2009)

If the plate is on top and out of the water it will weigh more than if the plate were underwater. 

Here is how it works:
Let's say a cubic foot of steel weighs 500 pounds on land and a bucket of seawater of the same size weighs 64 lbs.
This means if I take the 500 pond box of steel and place it in water it now weighs 436 lbs. I have 500 pounds pushing down and I have 64 pounds pushing up. So, if I add 436 lbs of lift I can make this 500 lb cube neutrally buoyant.

Add the plate to the bottom and the 1" will add to the buoyancy and will have the force of the water pushing up but with part of the box out of the water you do not get the entire 64 lbs of lift. Add the plate to the top and the entire 5 lbs is pushing down and this 5 lbs exerts more pressure on the bow than the weight on the bottom.

Having the plate on the top or bottom will affect draft but I am not sure how to calculate the difference.



bryson said:


> If the weight were shaped differently (say, a 6 inch cube, or really any shape where the cross-sectional area is less than 1 square foot as it protrudes from the box), then the draft would increase when it's on the bottom.


This I agree with but disagree in the same manner as above - the difference in displacement between under or out of the water.



bryson said:


> I don't know how much all that applies to designing float pods, though.


It matters because you questioned the benefit it the pod had a hole cut in the top. That's all.

The sides could be made from swiss cheese and the bottom solid and it would certainly help with wetted surface - ie: trim tabs


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## bryson (Jun 22, 2015)

DuckNut said:


> If the plate is on top and out of the water it will weigh more than if the plate were underwater.


The plate weighs the same no matter what, the only difference is that once it's in the water, you have the water pushing up on it. Might seem like semantics, but it's important. I know you already know that though, since you said this below:



DuckNut said:


> I have 500 pounds pushing down and I have 64 pounds pushing up. So, if I add 436 lbs of lift I can make this 500 lb cube neutrally buoyant.


Here's where things change:



DuckNut said:


> Add the plate to the bottom and the 1" will add to the buoyancy and will have the force of the water pushing up but with part of the box out of the water you do not get the entire 64 lbs of lift. Add the plate to the top and the entire 5 lbs is pushing down and this 5 lbs exerts more pressure on the bow than the weight on the bottom.


If the overall density of the box+plate assembly is less than that of seawater, the box will float. The force of the water pushing up is *always* equal to the volume of water displaced, regardless of where any weight is. Let's say you have an assembly that weighs 100 lbs and is 1 square foot. If you place it in water, it will sink since it only has enough volume to displace 64 lbs of water. As you put it, the assembly now "weighs" 36 lbs if it were on a scale underwater. However, if that 100 lb assembly has a volume of 2 square feet, it will float. It has enough volume to displace 128 lbs of water -- but it can't, since it doesn't have the weight required to do so. What will end up happening is that it will displace only 100 lbs of water, and the remaining volume will be above the surface. It's "weight" in this scenario would be zero, since the water is pushing up with the same force as the weight of the object.



DuckNut said:


> Having the plate on the top or bottom will affect draft but I am not sure how to calculate the difference.


If the plate is just a continuation of the box (say a 1 square foot plate on the end of a 1 cubic foot box), then the draft will be exactly the same. If the plate has a different shape, you can calculate the draft by figuring out the volume of the shape that will be underwater. For an object that floats, the volume of the part that's underwater will always equal the weight of the object divided by the density of the water. 



DuckNut said:


> It matters because you questioned the benefit it the pod had a hole cut in the top. That's all.
> 
> The sides could be made from swiss cheese and the bottom solid and it would certainly help with wetted surface - ie: trim tabs


I don't think that was me. I agree that if you had a hole cut in the top, it would be fine unless water started to spill into the box.

The whole thing about wetted surface and lift (lift from movement, not buoyancy force) is a completely different conversation.


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