Flatback Fireboat Rebuild

[CLM65]

That's perfect. I was worried about bow steer

Me too!!!!!

[Blue Agave]

IMO behind the fuel tank is a better location than in the bow. I believe what Matt meant by "Under the console" is "In the console", but that's just an assumption.

[RickK]

Rick, I know it's hard to visualize what my stringers will look like from that pic and the fact that the stringers are currently open.  This may help.  The dark border of the bilge is going to be Kay-Cell, while the hatched lines show the foam filled stringers.

Craig, I may be wrong but I don't think the little stringer in the middle behind the fuel tank is going to do anything for you as far as stringers go - it's not part of anything or contiguous front to back. It will help support the decking and keep the fuel tank from sliding back but that is all.  Those two things could be accomplished some other way, you could remove that and drop the water tank there.  The two complete stringers that you are tying into will take the longitudinal load.

Do you think the transom supports will give you enough tie-in to the stringers the way you're doing it?  If you look at most other rebuilds the stringers and transom supports are all inline, connected and contiguous to transfer load all the way front to back.

I also am thinking like Blue, that Matt was recommending "inside" the console. Kinda defeats all the space you're trying to free up in it by going under deck with the fuel tank though .

Isn't it fun trying to figure this out    I know you have the background to do it though.

[CLM65]

Good comments and questions Rick.  Here are my thoughts/logic (right or wrong).

1.  I know many people suggest just using two stringers, and eliminating the center and outer stringers during rebuilds.  After all, this is what Aquasport eventually did.  I'm not sure what year Aquasport did that, but I'm guessing it was when they went to a modified vee.  IMO (and this is purely my opinion), this makes more sense with the modified vee, as the shape of the hull is inherently stiffer than the flatback (due to the "V" versus a large relatively flat area).  So, while that little stringer between the bilge and tank area does not transfer load back to front, I believe it will add to the stiffness of the hull, as well as provide some support for the deck.  In any case, I don't think it hurts anything other than a little extra cost.  With that said, I will be removing part of it for the water tank.

2.  The way I am looking at the knees is that their primary function (again, my opinion) is to counteract the torque the motor is putting on the transom.  The force of the bracketed motor acts on the upper half of the transom.  Without any internal support, the transom would want to rotate about the transom-to-hull joint/axis.  The knees react to that torque, and transfer that force to the hull in a direction normal (perpendicular) to the hull.  The longer the reacting lever arm (in this case the horizontal leg of my knee), the lower the reaction force on the hull bottom (i.e., Torque = force x distance).  So I feel that the size and configuration of my knees should handle the force of the motor pretty well (i.e., minimize transom flex).  The other part of the stringer/knee function is to transfer load horizontally as you mention.  My sketch doesn't show it, but the fiberglass stringers are trapezoids, and will tie-in more substantially to the front section of the bilge than the sketch shows.  So yes, I think it will carry the load quite well.

3.  I guess Capt. Matt may have meant inside the console instead of under the floor, but that ain't gonna happen.  Even though I don't have a console yet, I can't imagine there will be enough room for the water tank, two batteries, etc.  I think below the deck is better for several reasons, such as lower COG, less usable space impact, etc.

I hope my thoughts make sense.  I know plenty of rebuilds have been completed differently than mine with great success.  But there are always more than one way to skin a cat.  And one of the pleasures I'm getting from this rebuild is the ability to be creative, think outside the box, do things a little differently, do things "my" way, etc.  If it wasn't fun, it would be hard to keep moving forward!

[gran398]

Makes good sense!

Also happy you can get the water tank beneath the deck.

One thing Matt touched on...because they are flat in the stern, there isn't much room under the deck back there...hardly any. These boats weren't engineered to have anything under deck, it was a closed bilge. No access, no pumps, nothing. Outer transom drain and external rubber plug...that was it back then.

So kudos to all of you guys that have rebuilt flatbacks...about the only place to put a tank (tanks) is forward, where the entry begins.

[RickK]

Good comments and questions Rick.  Here are my thoughts/logic (right or wrong).

1.  I know many people suggest just using two stringers, and eliminating the center and outer stringers during rebuilds.  After all, this is what Aquasport eventually did.  I'm not sure what year Aquasport did that, but I'm guessing it was when they went to a modified vee.  IMO (and this is purely my opinion), this makes more sense with the modified vee, as the shape of the hull is inherently stiffer than the flatback (due to the "V" versus a large relatively flat area).  So, while that little stringer between the bilge and tank area does not transfer load back to front, I believe it will add to the stiffness of the hull, as well as provide some support for the deck.  In any case, I don't think it hurts anything other than a little extra cost.  With that said, I will be removing part of it for the water tank.

2.  The way I am looking at the knees is that their primary function (again, my opinion) is to counteract the torque the motor is putting on the transom.  The force of the bracketed motor acts on the upper half of the transom.  Without any internal support, the transom would want to rotate about the transom-to-hull joint/axis.  The knees react to that torque, and transfer that force to the hull in a direction normal (perpendicular) to the hull.  The longer the reacting lever arm (in this case the horizontal leg of my knee), the lower the reaction force on the hull bottom (i.e., Torque = force x distance).  So I feel that the size and configuration of my knees should handle the force of the motor pretty well (i.e., minimize transom flex).  The other part of the stringer/knee function is to transfer load horizontally as you mention.  My sketch doesn't show it, but the fiberglass stringers are trapezoids, and will tie-in more substantially to the front section of the bilge than the sketch shows.  So yes, I think it will carry the load quite well.

3.  I guess Capt. Matt may have meant inside the console instead of under the floor, but that ain't gonna happen.  Even though I don't have a console yet, I can't imagine there will be enough room for the water tank, two batteries, etc.  I think below the deck is better for several reasons, such as lower COG, less usable space impact, etc.

I hope my thoughts make sense.  I know plenty of rebuilds have been completed differently than mine with great success.  But there are always more than one way to skin a cat.  And one of the pleasures I'm getting from this rebuild is the ability to be creative, think outside the box, do things a little differently, do things "my" way, etc.  If it wasn't fun, it would be hard to keep moving forward!

As I said, I knew you had the background to figure this out  

You're right, all the rebuilds are different in some ways. I was thinking that the forward force on the transom should push the whole hull as one piece - all solid from back to front.  I was going to keep the tank coffin as a square and come in with two stringers from the back and leave with two from the front to keep the span between them down but I figured there were too many pieces that could fail, Hence I went with the two long stringers although I cut into them a bit   . I still think they will be strong enough though.
The flooring will also help tie that all together and help the longitudinal strength but not as much I would think as the combo as long stringers and long flooring.  My 170 had 3 stringers so I went through this same thought process as you are and I also needed to get the console cleaned out so I could fill it again with other stuff   .  The stringers obviously also help stiffen the hull and help against twisting together with the decking. I am still entertaining putting one up front in the middle again.
Right or wrong I'll be the first to know after I take the first cruise  

[CLM65]

Rick,

If I could only say one thing about your boat...it would be that your stringers will be strong enough for anything you throw at it .  You are doing one heck af a job!

I appreciate your comments/questions/challenges.  I've never undertaken a project like this, so many of my thoughts and plans are unproven and are just ideas of how I think it could be done - not necessarily right, wrong, or better.  Well, hopefully not wrong.  But that's where you guys come in, correcting me where needed.

And thanks Scott - thanks to you, the water tank will be between the fuel tank and the bilge.  Good call (literally).  I just need to work out how I will route the fill and drain lines for the livewell (like yours), but that seems doable.  

[dirtwheelsfl]

If youre worried about stiffness between the tank and bilge sections, I would just sandwich a core of some kind in the bottom of the hull. A lot less work than building a stringer then cutting it to fit the water tank, and will leave a nice base for the tank too...    

3/4 nidacore is what id use, will conform to the hull nicely.


Whats the plan for joining the stringers to the new knee sections?

[CLM65]

Dirt,

That is a good idea with the nidacore...I just may do that

I'll try to explain my plan for integrating the knees into the stringers...on the sides of the bilge, the knees will form one side of the associated stringers.  The other side  of each stringer  will be the existing wall of the original stringer.  There will be a piece of composite board across rhe front of the bilge (basically a bulkhead).  The inner side of the original stringer, forward of this bulkhead, will be glassed to this bulkhead, much like it would have been glassed to the transom.  The stringers will then be filled with foam and glassed over the top.  I don't know if this makes sense???

[dburr]

So the knees will become part the inboard side of the stringers as you extend them to the transom..  GOOD idea and use of space!

With the water tank in the bilge, the vent hose should run under the deck and up to just under the washboard/gunn’l/cap.
There should be a loop seal (picture sink trap shape ie. U) then rise up to the shape of an inverted J facing aft with a screen on the end..  The idea is that all potable water vents should be inboard and screened to prevent particulates and contaminating fluids (gas/saltwater) from getting inside.

The loop seal is there so that in the event something splashes in it will not go straight into the tank.  The vent is below the fill so you can purposefully overfill the tank to;
1. Fill the loop seal.
2. Wash all the gop out of the vent line that was small enough to get through the screen.

The fill can be on the same side as the fuel fill, BUT must be higher than (up hill/forward of) the fuel fill.  The most IMPORTANT thing is that the fill for the water tank and gas tank MUST BE COMPLETELY DIFFERENT so heinous accidents by well-intended mates will not happen!!
Water fills normally require a spanner to open (female top) and have WATER stamped or cast in the fitting, and fuel fills on small boats are normally male and have FUEL stamped or cast on them…
  It might sound obvious but in a previous life as a yard rat I have had to change more than one water tank and have pumped a few diesel tanks….

All this is spelled out in a CFR someplace, I just can’t remember where..

Great progress Craig!!  

[Capt Matt]

After raising the deck the water tank will fit under the deck under where the console is, at least if the middle stringer is removed. This way your water fill, wash down pump and hose can be under or in the console too,
What do you think of the idea of using PVC pipes inside the pyramid stringers for water storage tanks?
They don't take up any room!!!

One of my main factors to remove the old stringers and go with a two stringer grid system was to gain all that storage under the floor along with making the whole bilge drain to the stern. With the old stringer system you loose so much storage and you will still have to cut drains thru the pyramid foam filled stringers. The last thing i ever wanted to deal with was wet foam again. If you want a bilge that can be laid out with live well pumps , bilge pumps strainers etc the middle stringer is in the way
There is no wrong or right way to build these boats it's all owner preference. Most people are not going to use there boats as much in a lifetime as  mine gets used in a year
Matt

.

[Capt. Bob]

What do you think of the idea of using PVC pipes inside the pyramid stringers for water storage tanks?
They don't take up any room!!!

Now you're thinkin' outside the box (or inside the trapezoid).
If you could fit a pipe with an ID of 4", 60" in length, you could fit about 6 1/2 gal of water on each side.

Excellent. Different but still excellent.

[CLM65]

Dave, thanks for the great info on the tank vent configuration.  As far as the loop seal, I assume the trapped water gets sucked into the tank when the tank level is drawn down and a slight vacuum forms?

Capt. Matt, great points and super suggestion on the PVC tubes inside the stringers!  I'm already running my rigging tubes inside the stringers, so not much room left for water tanks in there, but I guess there is no reason they couldn't go between the outboard stringers, right?  I would just need to figure out how to support them.  I've never had a freshwater tank before, so I'm not sure how much water I will need - the tank I bought holds 16 gallons...is that big enough or do you really think I will need more?

Capt. Bob, if you don't mind, I'd like to "cut and paste" your comment - excellent "outside the box" idea there!

Thanks guys!

[dburr]

Dave, thanks for the great info on the tank vent configuration.  As far as the loop seal, I assume the trapped water gets sucked into the tank when the tank level is drawn down and a slight vacuum forms?
Thanks guys!

Absolutely correct sir!!!

[Capt Matt]

What's your plan for the fresh water, just enough to shower to wash the salt off?
If so 10-20 gallons should be plenty even if taking a extended showeri with a female friend
I use a saltwater wash down to keep boat clean while out
Capt Matt