Are my toons too small? I need a game plan.

I have 1990 20' bass buggy - 60 HP Johnson - I think it weighed around 1275 lbs when sold but I cant find any manufacturing stickers (it might be 21'). I took off all the furniture that was on the boat when they sold it so the weight of 1275 lb is more likely closer to 875 lbs now.

I just moved to Florida and like going out for 3 days/2 nights which mean I have a lot of extra weight. I figure with batteries, gas, tackle, people, cabinets and so on I have about 1600 lbs added to the boat/motor weight. The floors rotten and the steering cables rusted so I figured it is time to restore the boat. With all my added weight around 1600 lbs + 875 lb boat/motor = 2475 lb that the toons need to support.

The pictures you can see the water level in front is 12" from the top of the toon and the back the water level is 6" from the top and this was with about 2100 lbs this weekend and with 600 lbs up front.

Will these 21" diameter toons be safe if I can even out the weight from the front to the back trying to get the water line more even or is it supposed to be lower in the back? Or would it best to add a 3rd center toon if I can find a 21” or should I replace the two 21" with 25" toons? I want to be as safe as possible particularity since I'll be in salt water and you never know what kind of wave might hit you from other boat or barge waves.

 

You seem to be piling an awful lot of weight on board for a 2-3 day expedition, the concern would be if it is all unfixed weights and in some unexpected happening it all migrates to one side of the boat, it could overwhelm the ability of one pontoon to support it. I think a good start would be to get an accurate fix on what it weighs as-is. You can fairly easily calculate the total buoyancy of the pontoon tubes, I would want it at least twice your gross load. The other thing that comes to mind is that you may be labouring this engine, under this load, and it won't last long doing that

 

Welcome to the Forum Howard - this is an impressive first post!

If you add a third pontoon in the middle to convert her into a trimaran, you resistance will go up significantly - not just from the frictional resistance of the extra hull, but also wave interference effects between the hulls. And as Mr E notes above, the outboard motor is already working hard as it is with the present load.

Ideally with a pontoon boat you should not let the draft increase beyond a maximum of half the diameter of the pontoons - your freeboard of 8" at the stern is not very much, and it would be much better if it was 11" or even 12".

If we disregard the effect of the 4' bow section, then the buoyancy provided by two 16' long and 21" diameter pontoons is approx 1,232 lbs at half draft (ie 10.5").

If you increase the pontoon diameter to 25", then the buoyancy provided by two 16' long pontoons at half draft (12.5") is 1,745 lbs - ok, the bow sections will add a bit, but not a lot, and we are still far short of your estimated displacement of 2,475 lbs.
And the cost of buying two 'new' 25" diameter pontoons is probably going to be significant in comparison to the current value of the boat.
Maybe you best bet might be to repair the deck and steering cables, and sell the boat, and look for a larger one for sale that has the required amount of reserve buoyancy?

 

I never thought about about unfixed weight shifting before but that's a good point especially since i'm in salt water now and might get hit with larger waves than i'm use to in a lake. When I renovate this or another boat i'll try to strap down the items.

I have also thought about selling this boat and buying a 24' pontoon which will have larger toons already on them. I think I would still want to renovate one anyway since I don't want the fancy seating and that would leave me with extra money to rebuild the motor and add another small motor or I'll look into a towing insurance now that I'm boating in the salt water and have no friends yet to tow me back (just moved to Panama City). 1600 lbs might actually be more weight that I actually have, just wanted to list more than less, I know with just the coolers, ice and batteries I have 427 lbs, I'm going to start observing how much battery and ice I really need since I throw most of my ice away from this weekends trip.

I guess another question I should be asking is which would be safer with this 1600 extra pound if I get hit by large waves, a 24' boat with 25" toons or this 20' boat with 25" or 3rd toon?

 

Thanks for the reply. You answered another question I had, is this 20' worth the main renovation or would it be best to buy a bigger pontoon. Since I will be looking for a 24' fixer upper and my approximate added weight might be 1600 lbs what's the minimum size toons I should be looking for on the 24' pontoon? I still will not have any of the stock furniture since I like a open deck so I wouldn't have that original 400 +/- lbs.

 

It is all very well calculating (or trying to) the minimum diameter pontoons required for a 24' boat - but not much use unless this size is available to buy 'off the shelf'.
Do you know what are the 'standard' sizes of easily available 'off the shelf' pontoons?

If your length went up to 28' where you have 24' of parallel mid-body along with a 4' bow section on each hull, then for a hull diameter of 25" and a maximum draft of 12.5" the buoyancy available from these sections (disregarding the 4' bow sections, which will not account for much really) is approx 2,620 lbs.
Note however that the material weight has also increased by adding an extra 8' of pontoon length.

 

I'll see if I can find some used pontoons later today and see what sizes they have on the 24' pontoons. I would think 25" would be the minimum size diameter but not sure.

 

You then are up for a bigger motor, my feeling is that if the existing bOat is too small, it would be better to sell it and buy a bigger one, rather than "grow" this one. I marvel though, at the loads you take aboard for a 2-3 day trip, I recall as a young fella we would go "bush" for the best part of a week with only what we could carry on our backs !

 

I definitely take a lot I already have a toilet I'd put a kitchen sink if I had room for it.
I looked at the tag located on the boat (picture above) and it says I can add 1200 lb or eight people well I took the furniture off which weighed around 400 so does that not mean I could have cargo of around 1600 lb on the boat? Maybe I could get rid of some extra weight I do go overboard and maybe I can shift the four deep cycle batteries up front, if I did that those numbers would probably change to 10 in from the top of the tune to the water level?

 

Stop overloading her. Never go past half the toon depth. A good captain knows the limits of his vessel.

The 21" toon should never or rarely be more than 50% submerged. Yes you were stern heavy. Yes, you were overloaded. The pontoon is simply too small for what you are doing and you need some bit of weight forward.

Noone here can really advise you to add a pontoon. The engine placement becomes an issue, for example. And noone can advise you to start changing toons. Really impractical.

Either find a way to reduce your load or get a bigger boat. I like to put coolers and bait tanks forward. They are easy to move to aft some for landing ashore. Same with anchors and other gearbags.

 

I just remembered I have the picture of when I bought the boat, the other owner had it sitting in water at his dock (I had to buy trailer). He had only the stock furniture, 1 battery and 6 gallon gas sitting on the boat full time and you can see the water line then (lime green line), it might have been sitting about 55% out of the water if balanced out.

Now with no furniture and all my 1300 lbs of gear this weekend (red line) it's about 43% out of the water if balanced out. Which if the tag say 8 persons or 1200 lbs I should be under the maximum weight by 300 lbs since I got rid of the furniture. So to be no more then 50% out of the water I can't go over 800 lbs gear?

I might unscrew the 4 plugs on top of the toons and just be sure there's no water in them?

 

Persons is 1200
Everything else is 380

A motor of 250 leaves you with 130 pounds for battery, coolers, fishing tackle, camping gear. Or, you reduce persons to say 4 people at 800 and pick up 400 pounds more gear.

The furniture should give you like 300 pounds more capacity, or 1880 total persons and gear unless the top and other stuff was added, then that comes off.

But you are either overloaded or sinking a holed toon at 6" showing

 

Howard, the bottom line is that for safety reasons you really should not be even approaching the stage where the pontoon is uniformly immersed at it's maximum width.
You mentioned that "it might have been sitting about 55% out of the water if balanced out" on the green line - and you really should not be immersing the hull more than 45%.
I think your best bet is to repair this boat and sell it, and then look for a bigger boat that has more buoyancy available to suit your particular requirements.
Or - build yourself a power cat - far superior to a pontoon boat in every way imaginable!

Edit - I just saw Fallguy's post above after I posted my note.
You need to have a good margin of safety available, and you need to plan for a worst case scenario - this could typically be where one hull still needs to have a good amount of reserve buoyancy even if all of the crew and stores / gear end up over on one side.
And you could add in a further safety factor by ensuring that you still have enough reserve buoyancy even if a compartment in one hull is breeched - I assume that each hull is subdivided into at least 2 or 3 watertight compartments?
Be aware that you start losing reserve buoyancy fast once the draft gets past the maximum width of the pontoon.

 

I'm just looking over options for now, I won't do anything unsafe and I know i'm not in a nice calm fresh water lakes anymore, I'm in bays of salt water now and don't want to get hit by the larger waves, so I know I can't go back out with the current setup.

I know a 24' would be best for what I need but I like the size of a 20' and I would hate to take a loss on this boat and no way do I want to renovate this boat to sell and have to renovate a 24' as well since my budget not more then $6000 since I'm going to buy a inshore boat for day trips as well. I figured I could buy 2-25" used toons for around $2000 (which I have found) and that would still leave me with $4000 for new flooring, cables and a tune up. But I've been told even with 25" toons it still would not work which is hard to believe?

I guess I'll look for an inshore boat first and think about the pontoons future later if 25" toons wont work on my 20' pontoon.

 

I am a bit confused about how you arrived 6" from the top.

seems a lot of immersion

maybe you need a shorter guest list or less stuff

we go canoe camping now and then and if winter, we take along a barge with a cooler full of stuff because the canoe gets overloaded

I'd focus on ways to reduce your gear. A big hundred pound generator is too much, for example.