Pontoon Boat & Deck Boat Forum

Hey floaters, looking to pick your brains... Years ago I added a third log under my boat (http://pontoonforums.com/viewtopic.php? ... 33#p160433)

Now how much additional weight capacity do you think could be reasonably added the the Coast Guard plate?

The boat is rated for 11 people @ 1495 lbs. Mathematically the third log adds roughly 4000 lbs buoyancy. Is there a formula or rule of thumb to calculate a safe additional load without risk of causing the "pontoon effect" and dumping my passengers? I feel like I'd be comfortable adding 1000 lbs, but science doesn't give a fawk about my feelings lol.

In August we're going on a boys boat trip and I'd like to max out on capacity without drowning my friends.

Thanks


LC.

Well I have a one year old 22 ft three log Harris and mine is only rated for 12.
Probably not what you wanted to hear....I think length is when the capacity goes up.

While there are specific formulas that the USCG would use to rate your craft if you simply look up similarly built craft you can get a reasonable ballpark idea. Looking up two different 22 foot tritoons I don't see them any higher than 12 people, 1,600 pounds people and gear and 2,400 pounds total motor, gear and people...

I don't have a solid answer, but it is intuitive that adding 50% in pontoon will increase your load capacity.

My approach would be to take a small increase when you have the well being and safety of others, in your hands. I certainly would not assume that you have an additional 1,000 pounds of capacity unless it's just you and bunch of equipment - but not people.

Your call of course.

Marc

riplipper wrote: ↑

Mon Jun 17, 2019 1:11 pm

Well I have a one year old 22 ft three log Harris and mine is only rated for 12.
Probably not what you wanted to hear....I think length is when the capacity goes up.

Would you happen to know what that 12 people is in pounds? My boat followed the old Transport Canada rules of ~136lbs/person, but they've since updated it to ~165lbs/person. I would imagine we're aligned with the US Coast Guard but not sure.

I also wonder if the manufacturers add an extra safety cushion for tritoons, given their higher horsepower rating and expected performance.

teecro wrote: ↑

Mon Jun 17, 2019 5:17 pm

While there are specific formulas that the USCG would use to rate your craft if you simply look up similarly built craft you can get a reasonable ballpark idea. Looking up two different 22 foot tritoons I don't see them any higher than 12 people, 1,600 pounds people and gear and 2,400 pounds total motor, gear and people...

Thanks, I can't believe I never thought to just check out comparable boats lol. I did this and used a bit of math, explained below.

Marc K wrote: ↑

Mon Jun 17, 2019 5:43 pm

I don't have a solid answer, but it is intuitive that adding 50% in pontoon will increase your load capacity.

My approach would be to take a small increase when you have the well being and safety of others, in your hands. I certainly would not assume that you have an additional 1,000 pounds of capacity unless it's just you and bunch of equipment - but not people.

Your call of course.

Marc

I'm always conscious of the boat's load and tally up rough weights in my head to get an idea, but it's difficult to do. Given cultural norms and my fear of mutiny, I've refrained from holding a notepad and asking each woman her specific weight.

However, I've done a bunch of calculations based on googled boat specs, their ratings and the volumes of cylindrical pontoons. By taking the total pontoon displacement and subtracting the weight of the boat/motor/fuel, then dividing the remainder by two (https://en.wikipedia.org/wiki/Pontoon_effect) to get the theoretical weight capacity, the USCG rating seems to be consistently 55% of that value.

For example, my boat with 2 logs (23"x22', South Bay allots 625 lbs for motors on boats rated for 115 hp) :

(~8000 lbs displacement) - (1800 lb boat) - (625 lbs allotted for motor/gear) = 5575 lbs remaining/2 = 2787.5 lbs theoretical capacity

2787.5 x 0.55 = 1533 lbs rated capacity (the sticker says 1495 lbs)


Now adding the 3rd log will obviously help, but I'm unsure how to calculate the pontoon effect value given that it's balanced right in the centre of the boat. Regardless, at even 70% of the boat's original capacity with only 2 pontoons, it should safely haul 2000 lbs (allowing for an ~800 lbs margin for my math). So taking the additional 3rd log with 4000 lbs displacement, and only using 12.5% of it (500 lbs) bumps the capacity up to 2500 lbs.



Yes this was a long post haha If you made it this far, does my simple math hold up or is it fatally flawed?

Adding a toon does not change the structure and size of a boat which is where the weight rating comes in.
Kinda like putting Class E tires on a 1000lb GVW trailer does not turn it into a 3000lb GVW trailer.
Look at most manufacturers and the weight capacity difference between identical pontoon and tritoon is maybe 150lbs.

LocoCoco wrote: ↑

Tue Jun 18, 2019 8:54 am

Thanks, I can't believe I never thought to just check out comparable boats lol. I did this and used a bit of math, explained below.

Honestly it does not matter how you do your math, your not gonna get more than 12 person capacity....

Again I'll comment looking at a brand new manufacture of a 25 foot, all 3 fitted with 25 inch pontoons and all three listed versions are the same model...
2 toon = 13 people @ 1830 / 2495 total
2.75 = 14 people @ 1970 / 2735 total
3.0 = 14 people @ 2025 / 2840 total

Legal rated capacity is just that, legal rated capacity. All the mods anyone does make no changes to the rated capacity. It's like adding air springs to a pickup. It doesn't increase the cargo capacity it just make the overloaded truck ride level.

If the authorities stop-and-frisk they’ll read the existing data plate the mfr'r placed on the boat and deny you any leeway if you’ve exceeded that capacity. So will the attorneys who sue you if someone is hurt. In fact, they may go after you if your modification was not approved by a marine engineer.
“Damn lawyers”, is what I say to my attorney daughter.