The right transom for a blue water yacht
Filip Sochaj, Krakens Head of Design, explains why blue water yachts need a reverse shear transom and how we improved it further.
It must be accepted that a blue water yachts design needs to incorporate some features that a regular cruising racer / holiday yacht may not necessarily need.
Now we can reveal that sometimes you can have the best of both worlds.
Whether you are recovering a man overboard, swimming, diving, cleaning the hull, cleaning fish, boarding the dinghy, unloading the provisions, taking a shower, or trying to get that perfect Instagram shot of breakfast on the water, the swim platform is a very important design consideration.
Builders and owners alike realised the importance of this long ago, but the dingy garage/drop swim platform solutions, as provided by modern yacht designers and builders, has raised some serious questions in blue water sailors’ eyes.
The “Classic” Reverse Shear Transom
The ‘sugar scoop’ swim platform is now a tried and tested solution. From a safety perspective, a place where we at Kraken always start, it offers the major benefit of providing by far the easiest and safest way of recovering a man overboard.
It’s an integral part of the yacht that is structurally uniform with the hull, so has the same durability and strength as the rest of the hull.
It’s swim platform is always ready to use, so presents no issues with stern-to docking or diver recovery. It is always ready to use, whether in port at anchor or at sea. When incorporated with davits it offers a fast and fuss-free launch and recovery of the dingy.
There is a couple of drawbacks though:
- The bottom swim platform will be quite restricted, even on quite large yachts
- It’s a quid pro quo with the stern lazarette, the bigger the swim platform the smaller the laz space
It’s a good solution because no element of it compromises the integrity of the hull and transom.
The dingy garage/swim platform
Most performance cruiser designs have gone down this route in the last ten years or so. It offers an aesthetically pleasing transom solution eliminating dingy davits by storing the dingy inside the transom.
With their sometimes huge bathing platform it’s a big selling point at boat shows, where people are thinking about their leisure time onboard. It does, however, come with some serious drawbacks and safety issues:
- If the transom door breaks off or becomes partially open the open dingy garage is then open to the sea. Whilst the sea cannot get into the main interior, the weight from the ingress of a wave into the dingy garage area will hold the transom down endangering the yacht due to swamping.
- At sea, and therefore when closed, the transom is a vertical wall, so recovering a man overboard is very difficult, as is recovering a diver or stopping for a quick swim unless its dead flat calm.
- Boarding the yacht when stern-to in a marina or at a quay can be difficult and requires a passerelle to be carried and deployed.
- You cannot lower the platform in any sea state other than dead flat calm. Wave slap or worse, waves going onto the platform, will wreak havoc on the hinges and support mechanism.
- Recovering and stowing the dingy if the sea has got up in the anchorage can be very difficult.
- The storage area of the dingy garage will seriously impact the interior aft cabin volume and eliminate the stern lazarette lockers.
- Deploying and recovering the dingy is a much bigger task.
All that being said it does provide a much bigger swim platform and eliminates davits.
Why not Both?
We all want to have our cake and eat it, so at Kraken we decided on trying to do just that with the K50 v2 transom.
We are totally committed to a reverse shear transom shape, since it’s by far the safest and easiest way to recover a MOB and the negatives that come with the swim platform/dingy garage are just too great.
Safety durability and ease of use are what Kraken Yachts are all about and we also didn’t want to sacrifice any lazarette volume.
Our base design was already a sugar scoop transom and a lot of work had gone into finding the right balance between the size of the platform and the impact on interior transom space, but we had to agree a bigger swim platform is desirable. We had to find a way to increase the platform size without reducing the internal volume. Many options were considered:
- The whole platform slide out like a drawer. While a good concept, this stumbled during the engineering analysis, where we realised that the hardware to achieve this might be too complex and therefore prone to breakdowns.
- A second “platform extension” slide out from underneath the sugar scoop. Neat and fairly simple but after further research, this solution was falling short on the same points like the one above, complexity and durability. As an added problem this solution meant there was an opening into the hull very close to the waterline, not good!
After going back and forth between discussions and the drawing board (well, computer really) for several weeks, the simplest of solutions came to our minds almost unanimously. Use a double leafed bottom swim platform and unfold it like a saloon table. Viola! Sounds too simple right? That’s because the base concept is just that. Imagine that you have a book the size of the transom platform, when you open the book you double its area. This is exactly what we did.
This solution achieved all our objectives:
- No openings into the hull – totally watertight and uncompromised integrity
- Full reverse shear transom for MOB/diver/swimmer recovery at sea in any wave conditions
- Double swim platform space when open
- Transom ladder moves with the platform meaning you always have a dive ladder no matter the position of the platform
- Simple and easy to deploy at anchor
- Enables the dingy bottom to be cleaned without the necessity to take it to shore, drag it up a beach and turn it over
The platform is supported by the hinge on one long edge with two Dyneema strops supporting the outside corners when deployed, thereby fully supporting the platform and the users. The Dyneema strops are connected to the davit tubes, from here the user can open or close the platform with a swift pull on the strops.
Flexiteek, teak or a non-slip covering on each side of the fold-out platform provides good traction wet or dry.
The dive/swim ladder design is our last innovation. The cherry on the cake. It is mounted to both parts of the platform so works equally well in either position. As an added bonus for swimmers of all ages, as well as divers with heavy dive tanks, the folded platform has two sockets either side of the ladder that house removable handholds, to make climbing back onto the platform very easy.
We are fitting this solution to the K50 currently in build so keep your eyes on the Birth of Blue Water Yacht for updates as it is constructed.