Pontoons vs not - another consideration?
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URL: https://www.fishing.net.nz/forum/forum_posts.asp?TID=90058
Printed Date: 16 Jun 2026 at 1:16am
Topic: Pontoons vs not - another consideration?
Posted By: Monsterbishi
Subject: Pontoons vs not - another consideration?
Date Posted: 14 Apr 2013 at 2:41pm
Being that the DNA thread is wandering a bit off topic:
Now here's something else to consider, my wording is a bit on the poor side, so bear with me: Pontoons only actually carry a buoyancy benefit when they are situated under the water line with water in/on the deck area itself. The downside to this means reduced deck space and mobility when compared to a non-pontoon of equal displacement, more physical mass situated at/above and further away from the center of gravity too. So friends, romans and forum folk - I ask the question: "What benefits does a pontoon boat actually have over one which has a equitable amount of buoyancy underneath the deck?" I recognise the perk that if you breach the hull space on a pontoon that you're not going to be sitting on the bottom afterwards, and that if the same happens on a non-pontoon it can turn it into a artificial reef - but is this not negated by either having a conventional hull with closed cell foam inside, or multiple bulkheads? What am I missing? |
Blindspot wrote:Replies:
Posted By: MarkE
Date Posted: 14 Apr 2013 at 3:01pm
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I don't see any real advantage over a regular hull with airtight compartments aside from the fact that it may stay upright if swamped... ------------- Sea Strike 18' Centre Console - Under Construction.... http://www.fishing.net.nz/asp_forums/sea-strike-18-build-thread_topic87723_page1.html" rel="nofollow - Build Thread here |
Posted By: CanadianJohn
Date Posted: 14 Apr 2013 at 3:04pm
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underfloor flotation will tend to turn the hull upside down. flotation in the right places will keep the hull upright and floating level. there are some good sources of info i've seen. maritime new zealand has a bit on this. so does US coastguard if you google it.
but you're right, it doesn't have to be a pontoon shape.
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Posted By: Fissure
Date Posted: 14 Apr 2013 at 3:26pm
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http://www.stabicraft.com/Buoyancy.aspx" rel="nofollow - http://www.stabicraft.com/Buoyancy.aspx |
Posted By: Monsterbishi
Date Posted: 14 Apr 2013 at 3:51pm
That's a inadequate comparison though, simply by making the hull shapes identical the performance characteristics largely fall in line with each other. |
Posted By: MarkE
Date Posted: 14 Apr 2013 at 4:09pm
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Yeah, funny how the "traditional" hull doesn't have chines.... ------------- Sea Strike 18' Centre Console - Under Construction.... http://www.fishing.net.nz/asp_forums/sea-strike-18-build-thread_topic87723_page1.html" rel="nofollow - Build Thread here |
Posted By: mouthu
Date Posted: 14 Apr 2013 at 4:11pm
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From my rather limited experience of owning a boat which just happens to be an aluminium pontoon boat....... and it isn't a stabi or frewza or one of the other many common pontoons out there. I'm glad I have a pontoon because I've already had my boat swamped.......... no biggie, bail hard with 20lts bucket till i have enough water out that i can motor and drain the rest through the scuppers. I'm also glad I have it as I heard last week that someone else with a stabi was hooked up on the rocks when the swell dropped and the transom went under the water, ........... also no biggie. Also when it was full of water, it was still very stable, no issues with it trying to roll over. And when at rest i can run (one step) from one side of boat to the other and it hardly moves. I've never owned a boat before this, so there's my thoughts. ------------- Yes it was me, I screwed it up for everyone. |
Posted By: noponies
Date Posted: 14 Apr 2013 at 7:32pm
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Indeed, the DNA thread has meandered. Maritime NZ have this pdf http://www.maritimenz.govt.nz/Publications-and-forms/Commercial-operations/Shipping-safety/Vessel-Stability-Guidelines-A4.pdf" rel="nofollow - http://www.maritimenz.govt.nz/Publications-and-forms/Commercial-operations/Shipping-safety/Vessel-Stability-Guidelines-A4.pdf which is an interesting read. Theres a more in depth take on the stabi info here; http://www.mymarine.com.au/stabicraft/stabicraft_advantage.htm" rel="nofollow - http://www.mymarine.com.au/stabicraft/stabicraft_advantage.htm I went with a pontoon for the lateral stability as well as the ability to take a swamping and not turn into a stone. What is probably required to really sort the benefits of a pontoon are the calcs for COB, COG and the righting force of a pontoon hull vs an equivalent non pontoon hull.
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Posted By: Monsterbishi
Date Posted: 14 Apr 2013 at 7:55pm
^^ That link is just a even more longwinded version of the stabi one, but it's just as pointless. Best as I can reckon, if you build a conventional hull with the underfloor flotation in the right spots as to minimise tipping when swamped - it's going to be every bit as effective as the pontoons on the stabi's without the loss of deck space or additional mass at/above the center of gravity. ie, the highly detail cad image that I have draughted up below: so that if it does take a wave, the water ends up in a bilge at the lowest point in the boat between two main flotation banks to provide stability, with the bow section separate to keep its nose up. akin to ballast really. Mathematically to become 'unsinkable' you would basically only have to provide the additional displacement of mass equal to the sum of the parts above the lowest open point of the hull?  |
Posted By: red89mx
Date Posted: 14 Apr 2013 at 9:59pm
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I think a smaller boat with boyancy in the floor will perform worse than a good pontoon when swamped, and possibly turn turtle....but stay afloat. I love pontoons in 5 m and smaller boats, but think the safety/stability benefits reduce as rig gets bigger. Totally swamped my old 4.8 pontoon at Karori light (through stupidity - tied off anchor line in full rip to a side stanction), and had water pouring over the transom to get out. with engine, scuppers and incentivised bailing was ok. Never felt in danger with boat sitting low in water - still stable and had steerage. As other posters had noted the main stability for a pontoon is the big chines formed where the pontoon joins the hull, |
Posted By: mouthu
Date Posted: 14 Apr 2013 at 9:59pm
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QUOTE]
[/QUOTE] bloody hell monsterbishi, if that's your level of drawing, i'd love to see your traffic plans. sorry to get off subject.
------------- Yes it was me, I screwed it up for everyone. |
Posted By: Ginger Roughy
Date Posted: 15 Apr 2013 at 4:06am
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Monsterbishi - I have to disagree mate. Whilst its definitely possible for a 'mono' to stay upright after a partial swamping, its most likely it will flip.. Although the likes of a flooding keel of the surtees etc would help a tad.. As with pontoons i can only speak with what i know which is senator, which have a large amount of their sealed air cavities right up inside the top of the gunwales, meaning once swamped would take a lot to roll. |
Posted By: Catchit
Date Posted: 15 Apr 2013 at 8:18am
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bloody monohulls are death traps !!
catamarans should be compulsory  ------------- "We gave Sir Peter a knighthood," Mr Key said, "And if we could give him a second one, we would." |
Posted By: Rodinator
Date Posted: 15 Apr 2013 at 8:37am
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That's right Ginger Roughy, with underfloor buoyancy only there is the potential for flipping if swamping occurs. But there is an alternative to pontoon hulls to achieve gunwale buoyancy. Here's a generic section, showing both underfloor and gunwale buoyancy within a traditional monohull. We've successfully used this arrangement for various designs from 5 -10m, recreational and commercial designs. The only issues are rod holders and wiring conduits  |
Posted By: Rodinator
Date Posted: 15 Apr 2013 at 9:01am
| Sorry I can't get the image to load |
Posted By: noponies
Date Posted: 15 Apr 2013 at 9:16am
Try renaming the image, without the '&' symbol and re uploading it.
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Posted By: Moki Marko
Date Posted: 15 Apr 2013 at 4:09pm
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agree with GingerRoughy & Rodinator - the difference with Rodinators's pic and mouthu's is the the gunwale pontoon (in R's pic) is above the waterline and it only comes into effect (as bouyancy) if the boat rolls far enough over- ie that buoyancy is very hard to push under the water - in mothu's (awesome) pic the u'floor cavities wil keep the boat on the surface if it swamps, but won't stop it swamping in the first place. As I have said - the guys who started the 'pontoon boats don't work' misconception were boat dealers who didnt' have a pontoon boat to sell - and somehow it's stuck |