# How raft tube diameter and rise affect handling



## blackfly (Mar 1, 2018)

As I look at rafts and the myriad of configurations available I am a bit perplexed. Could someone please explain when different tube diameter and rise compared between two similar length rafts become noticeable. What are the effects? Thanks.


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## mattman (Jan 30, 2015)

Well, I'll at least start ya out.
The main difference with tube diameter, is how much displacement you get. The more the displacement of water, the more weight a boat can carry, and keep the same amount of Draft, or how low in the water it will sit. Boats that sit higher, tend to be more manueverable, and float over more of the rocks in the river bed. They also will get surfed easier, catch more air currents and head wind.
When tube diameter becomes noticeable is a little hard to say, there are other variables, if it is a raft, then the width is one of those, since that to, affects displacement. It is basically a percent of the load capacity that would be noticed. On something like a 16' cat, I think you would notice the difference between 25 and 28" tubes in a big way, from what I've seen of friends that have them.
I will let others chime in on rise affect.


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## blackfly (Mar 1, 2018)

Thank you Mattman for your response. As I look at boats I am wondering how differently say a 14' boat with 22 inch tubes and 25 inches of rise will handle compared to a 14' boat with 19 inch tubes and 20 inches of rise. Then there are different types of floors to contend with as well. :shock:


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## curtis catman (Sep 29, 2015)

Tell us what you plan to use your new raft for and maybe that will give some insight into what type of boat would best suit your needs!


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## Electric-Mayhem (Jan 19, 2004)

Tube size and the rise are just two factors. Where the "kick" starts, the rocker profile and a bunch of other aspects of a raft make a huge difference in how it handles (plus width and such too). Add in diminishing tubes and there are A LOT of different options.

Honestly...the rocker profile of a raft probably makes the most difference in regards to how it handles and how much weight it will carry. The tube diameter won't really come into play until it gets loaded down quite a bit.

Generally, something with continuous rocker (the bottom has a constant curve) will be quicker and more maneuverable but may not carry its speed for as long, won't track as well, and won't carry as much weight as a raft with a flat rocker profile.

The Aire D series compared the Aire DD series is a good comparison between these. They both have diminshing tubes, but the DD (double diminishing) tends to keep the same profile as the R series rafts on the outside edge and the D series does both sides. The D series has continuous rocker and the DD has a flat bottom. They both can do double duty, but the D series rafts generally are used for paddle rafting or lighter gear boats and excell when you need speed and the ability to spin easily. The DD series, especially the 136DD and 160DD have very long and flat bottoms. For its size, the 136DD can carry a ton of weight but after a season and a half of using mine I find that its a bit slower and more prone catching waves then punching them.

So yeah...obviously you can get in really deep with this stuff. I think the important thing to note is that most of the times its gonna be personal preference and that rafts of a similar size will all be able to do similar stuff...they will just have small differences. To your most recent question...I think the difference between a 22 inch tube and a 20 inch tube will be minimal. The Rise (or kick) of the raft may be more significant, but will only really make a difference in how dry the ride is, how well it will ride over waves, and how much wind it catches. As I said already, other aspects of the rafts design will make a bigger difference.

I agree with Curtis...in order for us to help you the most it would help to get a description of what your intended use for the raft is and maybe a few specific models of raft you are looking at.


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## zcollier (Jan 1, 2004)

Thank you for asking the question. I've been thinking about this quite a bit and have been testing a few things lately. Here are some generalizations I've come up with for discussion:

1. For performance - bigger tubes are better. I'd like to see more 22" and 23" tubes. There probably isn't any problem with bigger tubes other than maybe air resistance.

2. The most expensive part of a boat is the fabric. I have a conspiracy theory that suggests that raft manufacturers like smaller tubes and diminishing tube boats to use less fabric for the same length of a boat.

3. One downside of larger tubes is that you have less interior room if the outer dimensions stay the same.

I'd also like to hear what you're planning to use your raft for.


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## blackfly (Mar 1, 2018)

I plan on using the boat for flyfishing on the rivers in Maine. There is some good whitewater on the Kennebec and Dead Rivers,but the big rapids can be skirted. I need a boat that will carry three people comfortably, but will mostly be myself and teen son. Perhaps an occassional overnighter, but mostly day trips. I am 6'4 with a wingspan of Kareem Abdul -Jabar. A lot of the rivers in Maine are pretty shallow. Hope this helps. What is the reasoning for diminished tubes?


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## mattman (Jan 30, 2015)

It might be wrong for fishing( don't fish, so don't really know) but I tend to think something 16' or 14' range, seems more comfortable for a big guy, with two other people. It would float higher in shallow water, and more room for overnights. If you are planning on a used boat, there are lot's of 16's in that neck of the woods, since that's the standard outfitter boat up there, or at least what I have seen on the Penobscot. Fishermen will have better info, however.

Zach, I agree with you on tube size, I would love to see larger sized tubes in more models, especially for boats that are meant for gear hauling. About 98% percent of my river time anymore, as a private boater, is multi day, and I really like having flotation, especially in Cats. I don't want a boat to ride low, punch into features instead of riding over, be sluggish, soak me in every wave on cold, winter time grand canyon trips.


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## blackfly (Mar 1, 2018)

I found this site that I found helpful in describing how boat design affects function.
https://triadrivertours.com/river-research/2018/1/13/13-foot-whitewater-raft-comparison-shootout


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## FlyingDutchman (Mar 25, 2014)

I highly recommend sticking to a raft in the 13 to 14 foot size range. 19 to 21 inch tubes will suit you well. Too big of a tube diameter makes it hard to get back in if your swimming. Rocker profile is not such a big deal, unless you plan to run steep drops, surf or R6+.

You’ll have to carry or drag your raft at most Maine put ins and takeouts. A big heavy 16 footer will be a hassle. Many paths will be narrow more suitable for canoes, and lined with poison ivy. You want a raft you and a buddy can carry into the good fishing spots. 13 foot rafts handle Dead or Kennebec River high water just fine.

I live in Massachusetts and have been rafting privately and commercially since 2006. I have an Aire Super Puma and a 13 foot Momentum (similar to NRS Otter 13 specs), a bucket boat, and formerly a mini max. With your long legs , a Super Puma will feel cramped. 

If you got the cash , go Hyside Pro 13 or 14, or NRS Otter 142, maybe Super Duper Puma 14 or 143D.


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## FlipLine (Jun 8, 2010)

mattman said:


> Well, I'll at least start ya out.
> On something like a 16' cat, I think you would notice the difference between 25 and 28" tubes in a big way, from what I've seen of friends that have them.
> I will let others chime in on rise affect.


I have 16' Sotar cat. The stock tubes are 24", and I sat way too low in the water when loaded up for a long trip. After doing the math to see how big a tube my frame (designed for 24" tubes) could handle, I had Sotar make me some 28" tubes - the diameter being the only difference. These tubes are sweet for carrying gear; but, as already mentioned they surf a whole lot easier. I was on a high water [6.5 ft] Middle Fork of the Salmon trip in May. Here's where it gets embarrassing; turns out none of us got left of Velvet Falls. i was not heavily loaded up with gear so I was stopped dead and was going backward faster than I ever had before when the boat behind me crashed in and pushed me out. He got out too. On the whole I really like my 28" tubes. But there is a price if you're not carrying the load you got them for.


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## Dr.AndyDVM (Jul 28, 2014)

Also, rafts have a floor, unlike cats. Tube diameter is a lot more important for cats because those 2 tubes are only things displacing water. Rafts have a floor which helps to displace more water and makes them more buoyant.


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## newpc (Aug 3, 2009)

Other thoughts not mentioned above: 

Taller the tube the more legroom you have, small tubes I feel like my knees are in my chest all day (6' tall here).

Diminished tubes...great for getting customers wet, horrible for fishing. You want to be able to stand up and brace your knees on the tube, cant do that in a diminished tube boat.

Materials: You have 2 choices, hypalon or pvc. Both have advantages and disadvantages. 

My Advice: Buy a decent used boat, (Avon, Aire, Hyside, Sotar, Maravia, NRS, Wing, RMR) and learn on it, and it will let you know exactly what you want from your new boat. You can always resell it for money towards your new boat. 

For what you've described I would say go for a 14' boat, big tubes, zero diminish.


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## elkhaven (Sep 11, 2013)

Most rafts marketed for fishing have diminished tubes.... not sure how they are horrible... either use a casting brace or better yet sit on an elevated seat with feet on the tubes and be stable and quick spinning back and forth to hit good looking water. Leaning into the tubes is how people fall out.... not that I don't do it on occasion but hardly a reason not to get a diminished tube boat. My diminished tube boat has 36" of kick...more than most normal boats. 

Hypalon, PVC, urethane, urethane bladder inside PVC, urethane coated PVC, urethane coated hypalon.... a number of material choices...all with pro's and con's.

Sorry to be argumentative but your information seems inaccurate too me.


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## newpc (Aug 3, 2009)

elkhaven said:


> Most rafts marketed for fishing have diminished tubes.... not sure how they are horrible... either use a casting brace or better yet sit on an elevated seat with feet on the tubes and be stable and quick spinning back and forth to hit good looking water. Leaning into the tubes is how people fall out.... not that I don't do it on occasion but hardly a reason not to get a diminished tube boat. My diminished tube boat has 36" of kick...more than most normal boats.
> 
> Hypalon, PVC, urethane, urethane bladder inside PVC, urethane coated PVC, urethane coated hypalon.... a number of material choices...all with pro's and con's.
> 
> Sorry to be argumentative but your information seems inaccurate too me.


We are all just posting our opinions based on our experiences. I've never had a "casting brace" or had to install an "elevated seat" to fish from normal boat. Nor have I ever had trouble staying in the boat in a normal tube boat, even hitting rocks or whatever and I fish class 4 royal gorge this way all the time. 

Come to think of it I have never seen anyone else take one of those type of fishing rigs down the gorge, but they may do it? If you're doing flatwater or small rapids then maybe diminished tubes with all that fancy extra frame stuff for fishing is the deal. 

If you want a boat that's good for tall people like the OP, and is good for fishing without all the extra frame stuff, while doing class 4, then you may not want dim tubes. Just depends on the use and the persons preferences I suppose. My opinion is that dim tube boats are horrible for tall people, based on my experiences. But I don't use all the fishing fram braces and seats and whatever.

Most commercial companies don't run dim tubes anymore, not that I see in my area anyway. They are uncomfortable, flippy, and cant haul as much weight.


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## blackfly (Mar 1, 2018)

Flyingdutchman mentioned access and he is accurate. Access here in Maine is not what it is in the West (spent most of my life in Montana). Weight is a consideration. Maneuverability is also important. I fished out of a cat a couple of Summers ago on the Yellowstone and it was super responsive and skated from one side of the river to the other. Are there rafts out there that act similarly? The last salesman that I talked to said that double diminished tube boats are what flyfisherman use now but could not give me a great answer to my "Why?".


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## elkhaven (Sep 11, 2013)

from my experience it's several reasons... first diminished tube boats have a rocker...and typically move over water more efficiently (i.e. independent of what the water is doing...more like a driftboat). Most fishermen want to move more slowly than the current, so doing so with less rowing effort is huge. That is the main reason I got a diminished tube boat (fishing is 90% of what I use my raft for) and they typically have less wind resistance, also a plus when you are trying to follow a specific line along a bank or keep yourself in one location. They are quicker - spin easier and are generally more maneuverable due to shorter water lines (usually). To me all of the above are what you want in a fishing boat. All of them are capable in class IV water, but if you were running numerous big rapids daily they may not be the best choice, if it's an occasional bigger III or IV they'd be just fine. 

There is no swiss army knife of boats...strengths on one hand equal weaknesses on the other.

Sotar makes a boat specifically designed by an outfitter in Montana for flyfishing...the Strike. It has relatively small tubes that diminish a lot, an almost flat top profile and a lot of rocker. They row like a dream if kept light but not a great overnight boat. Most other diminishing tube boats are compromises between this type of all in concept and normal full diameter tubes. 

In the long run the boat you get won't be a night and day difference... if you want to be able to haul it into rough or long access points then keep it smaller and simple - i.e. light. The most common fishing raft in my area (SW montana) is the super puma... by a very large margin. From what I've seen that sounds like a very good boat for your needs....


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## idaho_h2o (May 5, 2005)

blackfly said:


> Flyingdutchman mentioned access and he is accurate. Access here in Maine is not what it is in the West (spent most of my life in Montana). Weight is a consideration. Maneuverability is also important. I fished out of a cat a couple of Summers ago on the Yellowstone and it was super responsive and skated from one side of the river to the other. Are there rafts out there that act similarly? The last salesman that I talked to said that double diminished tube boats are what flyfisherman use now but could not give me a great answer to my "Why?".


Maravia Spider, you can't buy a more maneuverable raft. Also probably the best "skinny water" raft made. If it is big enough for you, it will treat you right. Has a little more depth than a super puma so works better for taller rowers. If you want something a little bigger look at the Ranger or Diablo, these are similar sized 14's just depends on if you want diminished or not. Streamtech has slight size variations of these boats if you want a complete package. Avoid I beam floors.


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## FlyingDutchman (Mar 25, 2014)

Maravia Spider and Super Puma very similar. Spider a little larger diameter tubes (19” vs 18.5”) and better quality ($$).

Diminished tubes help keep a low profile out of the way when casting. Moot point In my opinion.

Keep it light without a frame, just use paddles and an anchor to get to the good spots. Those big fat brook trout love hard to access places .


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## Electric-Mayhem (Jan 19, 2004)

Depending on how its designed, the double diminished tubes can make a bunch more room inside the boat as well. Some models reduce the outside of the boat to make it narrower with same amount of room inside the boat and others do it the opposite where the outside shape stays the same and the interior room is increased. You can see this in the D series vs DD series from Aire.


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## blackfly (Mar 1, 2018)

Lots of good insight. I think that I am getting a pretty good picture of the science behind the design of a raft from this thread and other readings. However, floor design still has me a bit puzzled. Anyone willing to discuss the merit of floor design? Pros vs. Cons.


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## elkhaven (Sep 11, 2013)

It will be an opinionated and ambiguous discussion. Lots of theories but since there aren't that many boats that offer both drop stitch and I-beam floors, real side by side comparisons are few and far between. In theory I-beams will track better but be harder to spin, the opposite for drop stitch. In general drop stitch are harder (can be pumped to higher pressures) and are easier to stand on. I have an I-beam floor but wanted drop stitch, I have no problems standing on my floor, especially if it's fully inflated - it's pretty damn hard. I'm not unhappy with what worked out for me. You will not see a night and day difference, but as you're fishing I would lean towards drop stitch but certainly wouldn't pass on a great deal on an I-beam floor.

For pure rowing efficiency, bucket boats rule, but you'll need a way to bail water out and hard floors for fishing. You can briefly stand on a standard (bucket) floor but you don't want to do if for long. Casting platforms and a floor in the captains bay are a must, but these boats will row with the least effort... They will also draft more vs a similar SB boat as a rule (inflatable floor offers more displacement as the standard floor, will flex up into the space below your frame components. This can be somewhat alleviated with a very tight fitting frame with dropped longitudinal rails (thus holding the floor more taught). think something like a cat frame dropped into the round boat. Lots of old frames built for bucket boats are built like this. Most newer frames for SB'rs are flat in profile, save a foot bar. I have a 12' hyside bucket boat that I occasionally fish out of so I'm offering direct observations.


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## raymo (Aug 10, 2008)

*Floors,,,,, pros vs cons????*



blackfly said:


> Lots of good insight. I think that I am getting a pretty good picture of the science behind the design of a raft from this thread and other readings. However, floor design still has me a bit puzzled. Anyone willing to discuss the merit of floor design? Pros vs. Cons.


Arriving back to the put-in from doing a car and bus shuttle, three cargo boats fully loaded and ready to go, I had my choice of which one to row, they were all 18 foot, except one was a bucket floor, one had an I-beam floor and the third was a drop stitch floor. Thinking of the river challenges for the day, types and class of the rapids, did I want to bail a boat today, do I want to do a full patch job or just pull out a roll of duck tape if anything happens to my floor, afternoon of strong winds and a good 6-7 hour day, the techniques of navigating each boat drew heavy on my mind. I was very tired from the night before. The only choice for me was the boat with the most beer!!! Pins and clips would of been my next choice!!! Try them all and after some experence, pick the one that workes best for you. Shooting from the hip thought, a good self-bailer would be my first choice. Have fun.


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