personalizing your boat | Port Townsend Watercraft BLOG

Altitude change and air buoyancy tanks

Ashlyn BrownDecember 12, 2024

Some emails cause our hearts to skip a few beats.

Checking in from our cross-country road trip. We stopped by a lake in Colorado a couple of days ago to take the PT11 out for a sail and noticed something very alarming... The back seat buoyancy tanks have bowed - like the air in the tanks expanded. They have returned to the normal shape again, but the fiberglass strips on the tank joints probably couldn't handle the pressure and have cracked - see pictures attached.

This boat was built at sea level in NYC and the tanks were expanded at roughly 10,000ft. The good news is that they did not explode nor do they appear structurally compromised, thanks to wood/epoxy as a construction method.

Most of our clients have used their boats near where they built them but others have taken their boats from sea level proximity to higher altitude lakes. (These two videos are thanks to Randy and Kim Kerr)

https://www.youtube.com/watch?v=jdLN_QaQrv4. Ross Lake (1,519 ft)

https://www.youtube.com/watch?v=LJV8MJJv6pU&t. Chilko Lake (3,845ft)

Randy replied to my inquiry about his lake trips: "We've never really taken our PT11 higher than 4000' and didn't notice any bulging in the buoyancy tanks personally. I could imaging customers that span 10K feet in altitude difference could easily see bulging or compressing."

Because Russell and I initially imagined our boat builders using their PT 11 dinghies primarily for ocean cruising, the influence of high altitude on the air buoyancy tanks simply did not come up but once in 15 years. That customer installed a relief valve but we never heard exactly what type or how well it worked. We imagined that as a one-off but we are also under the constraints of the USCG rules that prohibit access ports or any compromise of a sealed air tank if it is to be counted as buoyancy. Hence we moved on.

Times are changing however, and it appears that more PT 11s are on road trips and out lake sailing so, it seems prudent to address the air pressure question for anyone planning altitude differentials of more than 4-5000ft with their PT 11 or SPEAR dinghies.

There is an argument for drilling a 1/4" hole on the vertical face of each of the three air buoyancy tanks and filling them with thickened epoxy. (This keeps moisture from reaching raw wood.) If you then notice any expansion at altitude, you have a safe spot to drill a very tiny hole to relieve pressure. The hole could then be taped over until the boat was back at its normal altitude when the new hole could be filled. You would have to choose a time and place with a stable temperature to fill these holes. In an emergency, go ahead and drill tiny holes to keep damage from occurring. Just know that refilling those holes in a way that keeps the wood dry will be important.

One builder currently working on his PT 11 is planning to use it almost exclusively on mountain lakes and had already researched the pressure valve question before I reached out to ask about it. Have you heard of Gortex Dots? He has generously shared his in depth research and conclusions in this PDF article. An Idea for the Vented Volume Dilemma

The standard rule should still be noted for air buoyancy tanks: no access ports or compromise of the seal unless you plan to fill the voids with flotation foam. These dedicated air tanks (forward of the mast step and the aft seat boxes) are not intended as storage and using them as such could present a serious safety risk if you flood the boat. If you truly need to modify the design to fit your intended use, how you manage that is your responsibility, so be informed, do your own research, and think 'safety first'.

A review of the EP CARRY

Ashlyn BrownOctober 13, 2018October 13, 2018

This September we had the opportunity to play with an EP Carry electric motor for the first time. Dinghy owners often ask about an outboard for the PT 11.
Our preference is to discourage outboards on our dinghies because good rowing and sailing boats never make great motor boats. But some people really want to be able to use an outboard. That's understandable, but the fact is that the smallest gas outboard motors currently available are really too big for our boat; too much power and too heavy.

Now there is an option we can support; the EP CARRY electric "outboard". All of the technical information about this innovative little motor can be found on the website ELECTRICPADDLE.COM. Though it is compared to a 1HP on their website, it has sufficient power to get the PT 11 up to a cruising speed of about 4 knots. The USCG however, considers all small electric outboards as "2HP". Based on that formula, the PT 11 and PT Spear are rated for "2HP" so, the EP CARRY aligns with the Coast Guard figures. The amazing thing about this motor is that it weighs only 14.4 Lbs. This makes it very easy to mount and remove. The battery pack weighs 6.3 Lbs, making the total package less than 21 Lbs. There are several design features that add to the ease of handling as well.
(At this years wooden boat festival, Russell showed up with the motor in his bicycle bag.)

Our recent experience with the EP Carry was very positive and to my surprise, I caught Russell grinning after speeding off to visit other boats in the anchorage. "Mr. anti-outboard" was actually having fun and we enjoyed it further by taking a friend on an evening "cocktail" tour of Reid Harbor, a deep bay with lots of shoreline and many boats to observe.
We spent a couple of days, driving along the shore of Sucia in the San Juans, in Shallow Bay making watery doughnuts, backing up, going forward, generally goofing off, and then venturing out to 'Danger Reef' to "brave" close proximity to a group of Stellar Sea Lions. We were pleasantly surprised by how far the battery went on one charge. You will notice in our video that we carried our oars with us but we did not need to employ them.
This motor is not silent. Neither is it loud. Our lightly built plywood boat seemed to acoustically amplify the sound a little. Even so, there was no need to raise our voices for conversation. In fact, we could almost whisper and still communicate. This was a plus to me. Loud outboards in quiet anchorages are, in my mind, a real nuisance and many of us are familiar with boaters talking in their loud dinghies barely hearing each other and assuming no one else can hear them either...but of course we hear every word. Sound is a funny thing. With the EP Carry, the birds, seals, and sea lions were undisturbed by our passage. It made it a great modus for exploring the nature around us.
Another thing that is really attractive to us about this motor, is that even with our limited house battery power, we could re-charge the EP Carry Battery. It does require a 150-200W inverter, but this lithium battery requires a third of the power than comparable models to recharge. At home, it is simple to plug it into a normal outlet. Beyond charging the battery and rinsing the unit after use in salt water, there is virtually no maintenance. Yet another plus.
(see our video exploring Sucia with the EP CARRY)
When our EP Carry arrived at the door, unpacking it was quite amazing. The care taken to pack it and the detailed contents made for a well thought out and complete package. It was a positive reflection of Joe and Linda who have spent years perfecting their product. They, like us, had a vision that they worked and reworked in every detail. In fact, the original mount did not fit the PT 11 and now it does. Further, the EP Carry, designed right here in WA State, is assembled in the USA. It is yet another example of admirable American ingenuity with style and a small business making a positive difference in the world. Of all the outboards on the market, we feel confident that the EP Carry is a good fit for the PT 11.

USER MANUAL PDF

Builder modification consideration

adminNovember 20, 2013Leave a comment

Russell and all of our design consultants have a lot of experience with wood and epoxy boat building and a lot of thought and science went into making sure our boats are designed to be both light and strong. No boat is indestructible of course, but please consider carefully any modifications and feel free to consult us if you have concerns based on your planned use of the boat. We may not have a full time tech line but we do try to be available for customer concerns.
There are lots of ways to personalize your boat but please do not attempt to alter the structure. Also, a well built Pt 11 is a valuable boat and modifications could negatively affect resale value.

Boat building is a creative process. With our kits, it may be said the Russell has thought of 'everything' and thus, the margin for builder inventiveness is limited. I beg to differ and I have great faith in each person's ability to creatively personalize their boats! It is also our hope that the building experience in itself serves the creative spirit well and the end result is a boat that makes the builder proud and happy. It is difficult to make guarantees, and especially so if any part of the design and/or the described building method, is omitted or modified.
In reference to some questions we have received ;
Flotation vs Storage; about the PT 11: The three compartments, one in the bow and the two in the stern, are completely sealed flotation and have the same value as foam flotation in this type of boat. If access ports to flotation compartments are installed, equal foam flotation would then be required to replace the sealed air. This would be a lot of work and totally pointless. Trying to use designated flotation compartments as storage can be dangerous if the boat flips or floods. On the PT 11 & Spear, there is a large storage aft of the mast step with ample space and the PT Skiff has 3 separate storage areas. We had to calculate flotation for the PT11, the non nesting PT SPEAR, and the PT SKIFF in order to satisfy the USCG safety guidelines. It is the builder's responsibility to abide by those rules, and, it is just plain smart.

Re-enforcements; Any additional wood or glass than what is prescribed in the manual, serves to add weight and will not necessarily make the boat any stronger than designed. Our boats are already designed with heavier glass on the bottom and solid fiberglass caps on the skegs for added toughness. If it is expected that the dinghy will be typically dragged over rough landings rather than carried, one could beef up the fiberglass on the bottom further, but it will add weight.
The transom, as designed, is strong. The rudder is a kick up rudder so there should be no chance of ripping off the transom of the boat with this rudder. If you plan to use a small outboard, (max 2HP) you would use bearing strips on the outside and clamp pads on the inside.
Builder resources; Our PT 11 family is growing. This is very exciting for us as we are a small company of just Russell and myself. Even more exciting is that our customers have been building beautiful boats! This year, 2013, we established a registry of sorts (see the map) as an owner/builder resource and aim to create an interactive community. (see our Builder Center page) The questions, comments, shared experiences of each builder are all welcome material that I will look forward to adding to the blog for others to learn from and enjoy. Our heartfelt thanks to our customers, followers, and friends who share their opinions and enthusiasm about our products. We would not be here without you.

PTW Ashlyn