[finesse]

I finished the restoration of a 17' Mako Classic two years ago, replacing the stringers, deck and transom. I'm happy to share my thoughts on this experience with anyone who is taking on any of these activities.

I did all of this work sensitive to the fact that Mako hull is quite good under power, but is marginally self-bailing at rest, particularly with a four stroke. With all of the changes (I also moved the new gas tank forward a bit, and put the battery up front) the boat rides quite well, but still does not have enough margin between the self-bailing transom drains and the waterline. I dock in a tidal area, and heavy rains combined with strong tidal flows lead to challenges.

I'm planning to build and install flotation pods from marine ply/epoxy/glass to raise the boat 1 to 2" at the aft waterline. I've read a bit about the mechanics of the aluminum pods on jonboats, and most experiences seem to indicate an improvement in performance as well.

I've attached a picture of my design. If you've attempted something similar, I'd be interested in your thoughts.

 

[bryson]

So essentially hull extensions (sponsons)? If you maintain the same running surface back, you should be able to find lots of info on this forum if you search "sponsons" or "sponson debate".

I'm assuming the scuppers drain the cockpit only, and the cockpit not connected to the bilge in any way, correct? If that's true, I will say that if your scuppers are slightly underwater at rest there won't be an issue even without the sponsons. For example on my Hewes the scuppers are right at the waterline with nobody in the boat. If I sit in the boat with the scupper plugs out, the water will come into the cockpit maybe an inch, then find its level and stay there. In theory you should be able to leave the scuppers open without any issues.

That being said, I don't know exactly how your boat is laid out, so this may not apply to you. I did think about doing something similar to my Hewes, not necessarily for the self-bailing feature but more to get back an inch or two of draft. Up to this point I have felt that the return wasn't worth the effort.

 

[Smackdaddy53]

You’re not gaining an inch or two of draft with sponsons unless they are ungodly huge. You have to remember you’ll only gain by what’s below the water line. They’ll help a little with draft but more with stern squat on hole shot and squeezing water to the prop.

 

[bryson]

You’re not gaining an inch or two of draft with sponsons unless they are ungodly huge. You have to remember you’ll only gain by what’s below the water line. They’ll help a little with draft but more with stern squat on hole shot and squeezing water to the prop.

That's true -- I hadn't even looked at the dimensions in the picture. If he's assuming 10" draft, those are maybe a touch over 100# of flotation (figure around 150# of displacement, minus the 50# of materials and crap used to make them). Doubtful it would lift the stern enough to get the scuppers up.

If the pods are used as a running surface, they will need to be able to transfer a good bit of load back to the transom, so they will need to be built and attached with that in mind. Also worth noting is that if he has tabs, they will need to be relocated, and he will need to build access to be able to at least run the wire, if not through-bolt all the hardware.

Good point about stern squat on hole shot too. On that thought, I imagine it would also make it (only slightly on a larger boat) more difficult to get the bow up in nasty water. Sometimes you get stuck in a situation and need to "mush" through the waves. Anyway, now I'm turning this into a plain ole sponson conversation

 

[Smackdaddy53]

That's true -- I hadn't even looked at the dimensions in the picture. If he's assuming 10" draft, those are maybe a touch over 100# of flotation (figure around 150# of displacement, minus the 50# of materials and crap used to make them). Doubtful it would lift the stern enough to get the scuppers up.

If the pods are used as a running surface, they will need to be able to transfer a good bit of load back to the transom, so they will need to be built and attached with that in mind. Also worth noting is that if he has tabs, they will need to be relocated, and he will need to build access to be able to at least run the wire, if not through-bolt all the hardware.

Good point about stern squat on hole shot too. On that thought, I imagine it would also make it (only slightly on a larger boat) more difficult to get the bow up in nasty water. Sometimes you get stuck in a situation and need to "mush" through the waves. Anyway, now I'm turning this into a plain ole sponson conversation

I drew up my designs and had Boyd’s Welding fab aluminum sponsons for my aluminum hull and they worked great.

 

[finesse]

So essentially hull extensions (sponsons)? If you maintain the same running surface back, you should be able to find lots of info on this forum if you search "sponsons" or "sponson debate".

I'm assuming the scuppers drain the cockpit only, and the cockpit not connected to the bilge in any way, correct? If that's true, I will say that if your scuppers are slightly underwater at rest there won't be an issue even without the sponsons. For example on my Hewes the scuppers are right at the waterline with nobody in the boat. If I sit in the boat with the scupper plugs out, the water will come into the cockpit maybe an inch, then find its level and stay there. In theory you should be able to leave the scuppers open without any issues.

That being said, I don't know exactly how your boat is laid out, so this may not apply to you. I did think about doing something similar to my Hewes, not necessarily for the self-bailing feature but more to get back an inch or two of draft. Up to this point I have felt that the return wasn't worth the effort.

Bryson - thanks for the tip on searching sponsons...I'll take a look. Also, you bring up a good point...currently any overflow into my deck drains into the bilge where there is an isolated compartment in the stringers with a bilge pump; I re-used the stock Mako opening for that compartment which includes a small channel to drain deck water into the bilge. That makes the bilge pump more critical than I want it to be. When it is docked, I can't think of a scenario where I would want to have any water drain into the bilge. As long as the boat floats well with the scuppers open, it will always as you said it will find it's natural level, and I should be ok.

 

[finesse]

You’re not gaining an inch or two of draft with sponsons unless they are ungodly huge. You have to remember you’ll only gain by what’s below the water line. They’ll help a little with draft but more with stern squat on hole shot and squeezing water to the prop.

I think you're right in terms of the overall draft. This boat sits down a little in the stern at rest; I'm hopeful that sponsons will bring the stern up a bit at rest. For instance, adding a 100lbs. to the bow has the desired effect in terms of moving the waterline at the transom.

 

[bryson]

Bryson - thanks for the tip on searching sponsons...I'll take a look. Also, you bring up a good point...currently any overflow into my deck drains into the bilge where there is an isolated compartment in the stringers with a bilge pump; I re-used the stock Mako opening for that compartment which includes a small channel to drain deck water into the bilge. That makes the bilge pump more critical than I want it to be. When it is docked, I can't think of a scenario where I would want to have any water drain into the bilge. As long as the boat floats well with the scuppers open, it will always as you said it will find it's natural level, and I should be ok.

Wait, so the cockpit drains to the bilge? What do the scuppers drain?

 

[finesse]

That's true -- I hadn't even looked at the dimensions in the picture. If he's assuming 10" draft, those are maybe a touch over 100# of flotation (figure around 150# of displacement, minus the 50# of materials and crap used to make them). Doubtful it would lift the stern enough to get the scuppers up.

If the pods are used as a running surface, they will need to be able to transfer a good bit of load back to the transom, so they will need to be built and attached with that in mind. Also worth noting is that if he has tabs, they will need to be relocated, and he will need to build access to be able to at least run the wire, if not through-bolt all the hardware.

Good point about stern squat on hole shot too. On that thought, I imagine it would also make it (only slightly on a larger boat) more difficult to get the bow up in nasty water. Sometimes you get stuck in a situation and need to "mush" through the waves. Anyway, now I'm turning this into a plain ole sponson conversation

Bryson - I came to the same calculation regarding added buoyancy. I agree that there will be quite a bit of load, and I'll have to attach by bolting through the transom. The boat runs well in smooth water now, and is very controllable, though wet, in rough water. Where I fish, we're often dealing with rough water, we don't have to run very far but we fish where there's often confused chop.

 

[finesse]

Wait, so the cockpit drains to the bilge? What do the scuppers drain?

dec
Ya., it's a bit different. The scupper, which is really a 1" drain hole with a collecting drainage area does primarily drain the cockpit. Just forward of the transom there's a hatch to the bilge. The hatch has a cover that seals the hatch except for a small channel (purposely built). Water on the deck drains primarily through the scupper. When water gathers in the stern, it finds the channel and drains to the bilge. I thought this was a good idea and cut it out of the old deck and fitted it on the new deck. I think that setup, and the occasion of rain and tidal flow backing water up at my stern cause that setup to get overwhelmed. I've had two incidents in the past year; one where it was clear that there was more than normal water in the stern of the boat but the boat seemed to "catch back up" on it's own, and a second incident where the marina used a portable pump to drain the water. I'm going to add more foam flotation below decks where-ever I can to reduce the additional loss of flotation when this happens, make sure that there is no way for water to get from the deck to the bilge, and possibly add sponsons...

 

[bryson]

Looking at some pictures of the Mako 17, it sounds like you are using the term "deck" and "cockpit" to mean the same thing, right?

I'm having trouble picturing the hatch that is intentionally not water-tight. I think that you should either drain the deck to the bilge and rely on the bilge pump (no scuppers), or keep bilge as sealed as possible to allow the deck to self-bail.

It sounds like some of the issues you are having could be addressed without adding sponsons. You may want to add them anyway, but I would try to remedy some of these other things first.

 

[finesse]

Looking at some pictures of the Mako 17, it sounds like you are using the term "deck" and "cockpit" to mean the same thing, right?

I'm having trouble picturing the hatch that is intentionally not water-tight. I think that you should either drain the deck to the bilge and rely on the bilge pump (no scuppers), or keep bilge as sealed as possible to allow the deck to self-bail.

It sounds like some of the issues you are having could be addressed without adding sponsons. You may want to add them anyway, but I would try to remedy some of these other things first.

Yes., by cockpit, I meant deck. I agree; based on the feedback from this thread, I do think I will make the hatch watertight first, and add more flotation in the bilge area. I'm in New England, and so we have a relatively short season, and lot's of time to fiddle in the winter, so I may take on the sponsons as well.

 

[State fish rob]

Sponsons on my well boat do not follow hull line , slight taper upwards 1 1/2” over 48” starting at the transom. Fiberglassed a wedge into each to help w holeshot/ stern squat.
Just curious, what motor are you running ? Ive worked wonders on flats boat w new lay out to adj balance. Biggest diff was moving tm batteries to bow ,getting cranking battery under console centered , not in rear port hatch. My motor( f50 ) tilts clear now.