Is your swim deck structurally strong enough to support our Tilt-Up PWC Rails?
This page focuses on welded houseboat swim platforms and their ability to support our Tilt-Up Rails. But the same techniques can apply to smaller boats with bolt-on platforms if you are concerned about its ability to support the Cross-Deck mounting system. If you are concerned about your swim platform's support strength, feel free to email me at sales@divnick.com. Please include photos of your swim deck including the top side and underside if possible, along with the size of your houseboat or cruiser.
Most modern 3-seater PWC’s are just under 1,000 pounds. With our Rail design, almost all of that weight is leveraged (cantilevered) beyond the swim platform, so it multiplies that weight into downward force on your swim platform and the rear of your houseboat. The welded aluminum framing under the swim platform on most standard-construction houseboats is structurally strong enough to support that force. We define a standard construction houseboat as typically having a full aluminum hull with the swim platform integrally welded on the back with welded aluminum framing supporting it underneath. Examples would be Sumerset, Stardust, Thoroughbred, Lakeview, Horizon, Destination, Sunstar, Jamestowner, and others.
Here is a sample photo of the underside of standard aluminum hull houseboat construction.
In addition to the framing support underneath, the sides of most houseboat swim platforms form upper and lower "triangular side gussets" as part of the hull as shown in the inset below. Triangular gussets add significant strength. The main picture below is of a swim deck with no upper or lower side gusset supports. So they added one chain-gusset and mounted the PWC Rail Frame next to it. The chain is bolted down through the main deck floor and the other end goes around the back edge of the swim platform and bolts to the frame underneath. This is inexpensive (less than $20) and very easy to do with a drill and simple hand tools. No welding or fabricating of angle structures is required as discussed in more detail further down this page.
A gusset strengthens the connection between the swim platform and the rear deck.
Another kind of force is along the back edge of the swim platform that could “bow” it downward under the Rail tubes. That load-force can be strengthened by spreading the load out with a 2-foot piece of aluminum-angle bolted over the rear-edge of the swim platform, as illustrated above with the “Optional Aluminum Angle” caption. The PWC Rails are 16.5 inches wide, so spreading that load out to at least 2 feet can make big difference…especially if that 2 feet reaches some framing support underneath. If 2 feet doesn’t reach the framing, then you can use a longer piece. This is typically not necessary for a standard construction houseboat. It is more likely needed for an add-on swim platform.
If you want to add aluminum angle, we recommend 6061-T6 alloy, 1/4 inch thick with the 2 inch side on the top of your deck and a 3 inch side down over the back. You can get this for about $20 on https://www.metalsdepot.com/search?q=A33214 or any local aluminum supplier.
Structural Strength Consultation: If you are concerned about the structural strength of your swim deck, you can get in the water and take some pictures of the under-structure and send them to us. We will gladly offer our feedback and opinion. Please include photos of the portion where the vertical wall of the swim platform connects to the swim platform and where it connects to the outdrive ceiling, along with photos similar to the one above. You can send pictures to sales@divnick.com
We will gladly offer our observations, but ultimately, it is your responsibility to determine whether or not your swim platform will support the force that will result from using our PWC Rails.
Floatation Angle
Generally, even relatively small welded aluminum houseboats that are about 50 feet long by 14 feet wide will handle the weight. Obviously, the smaller your boat, the more effect a PWC will have in terms of lowering the rear of your houseboat in the water which is a separate issue from the swim deck's structural strength. Of course, that would affect the way your boat cruises. But even if the aft end of your boat squats in the water quite a bit, that might not matter to you, depending on your goals. If you just want to get your PWC out of the water for storage, then you won't be as concerned with how it affects the level of your houseboat because you will unload your PWC before using your boat. Most of our customers with small houseboats unload their PWC when they are “living” on their boat so the beds and counters are more level, and so it will cruise better when they take it out. They just want their PWC out of the water when they are away...and not have to pay extra for a slip or have to trailer it back and forth.
Cross-Deck Models
If you have a bolt-on swim platform or fiberglass hull, it might not be strong enough to support the leveraged weight of our Tilt-Up Rails. If you have a yacht, cruiser, or any boat that is shorter than 50 feet, our Cross-Deck Models might be the best solution for you.
Adding Structural Support
But if you want to use our Tilt-Up PWC Rails and you think your swim platform might not be strong enough as it is currently configured, there are some ways you can add support that would significantly increase the structural load-capacity of your swim platform. Because of the variety of shapes and angles, we don’t provide kits, but we would be glad to provide our feedback.
Let's take a look at some types of gusset supports. They are divided into two types: Above-Deck Supports and Under-Deck Supports. Notice that the second photo in the left column is a cable. In other words, it doesn't have to be a fabricated stiff tube or angle shape that is welded to your boat. It can be a cable or chain.
There isn't a good way to add an under-deck triangular gusset support to houseboat swim platforms because there is no hull under the swim platform against which the gusset can be affixed. Some people mistakenly think that the engine transom wall is under the swim platform. But the picture at the top of this page and the drawing below shows that the forward wall of the swim platform is NOT the transom wall.
The outdrive area is between the transom and the swim deck wall. The most significant way to strengthen the structural support of the swim platform is to add framing under the outdrive ceiling that connects to the framing under the swim deck. However, adding framing underneath is complex, would all be custom, would require you to pull your houseboat out of the water so it can be welded, and would therefore be very expensive. The good news is that adding gusset support above the swim deck as illustrated by the red dotted line can be simple and cost very little.
There is no question that welding gussets is stronger than bolting them. But that is also more expensive. If you are going to have something welded, then you would have triangular gussets made that fit your vertical swim platform wall height and the front-to-back depth such as the ones shown next.
It should be noted that gussets like this lock the platform and vertical wall together. But it doesn't strengthen the angle where the outdrive ceiling and vertical wall meet. Triangular gussets in that corner underneath would add a lot of structural strength.
The downside of an above-deck support is that it remains in place and has to be stepped over. But that is relatively minor compared to what you gain.
Simplest and Least Expensive Solution
Using chain as an above-deck support is the simplest and least expensive option. This option doesn't require you to have aluminum tube or flange gussets fabricated, doesn't require welding, doesn’t require complicated measurements, doesn't require you to pull your houseboat out of the lake, is easy to install, and only costs a few dollars. The accompanying picture shows a 51 inch heavy duty chain at Walmart for less than $15. It is considered a "1/4 inch" chain which refers to the gauge of the link. It has a 3500 pound rating. These "trailer safety chains" are available at every hardware and auto parts store. You can easily fit up to a 1/2" bolt through the links in most trailer safety chains.
Or you can buy 1/4" chain by the foot at most hardware stores for about the same cost. However, chain-by-the-foot usually has smaller links which reduces the size of the bolt you can use.
A single chain can increase the load-capacity of your swim deck by over 3,000 pounds...for less than $20!
For just a little more cost, you can make the gusset out of "aluminum-angle" like the sample image below. You can get any length aluminum angle from https://www.metalsdepot.com/search?q=A32316 or any local aluminum supplier. We think this looks more professional, but is a little more difficult for most people to cut and bend...although it can be cut with a hacksaw and bent in a vice fairly simply.
You will want to affix the gusset beside at least one side of your PWC Rail Frame. Some people add a gusset on both sides. You will want to bolt the gusset through framing on the underside of your deck if you can. So you will need to swim under your deck to select the location, and you will then select the bolt length so it is long enough to go through the gusset, the aluminum skin of the deck, the framing, a washer, and the nut with at least 1/4 inch of additional length. You can buy the bolts, nuts, and washers from a hardware store. We recommend at least 3/8" bolts in whatever length you need. Stainless steel hardware will work. Galvanized hardware is even stronger. Be sure to use lock washers, or nuts with self-locking nylon included.
If there is no framing where you want to affix your gusset, then add a piece of aluminum or galvanized angle from a hardware store, cut it as long as will fit under where you are bolting your gusset, and run your bolt through it. This will spread the load out more than a simple washer. Alternatively, you can use a piece of treated 2x4 or 2x6 wood, but you might have to replace it every few years.
The upper gusset anchor-point will be stronger if it is through the floor of the porch deck rather than the vertical wall of the swim platform so it will be as high as possible and will "pull" against the entire floor. You could anchor it as high up as possible on the vertical wall, but the additional 1 inch or more of height and the pull against the porch floor is much better. If you have a canvas railing around your rear deck, do not anchor the gusset to the tube railing which is not strong enough to offer much support.
The lower end of the gusset should be anchored as far to the rear of the swim deck as possible...even better if it goes around the edge and bolts to the framing underneath as shown in the photographs above. If the framing under the deck doesn't line up with the framing through which you anchor the top of the chain, you can add an aluminum or galvanized angle and place it under the rear of the deck and affix it with the same bolt that anchors the gusset. That will spread the support out beyond the bolt.
If you use a chain gusset, you will want to drill and bolt one end first, but don't tighten it all the way...leaving 2 or 3 turns for tightening after you affix the other end. Then stretch the chain out and drill a matching hole for the other end so that when you feed the bolt through the chain and newly-drilled hole, it stretches the chain as tight as possible. As you tighten both ends, it should pull the chain even tighter so it becomes a strong gusset supporting the rear of the swim platform.
If you use an aluminum-angle gusset, you don't have to be concerned with that...you can drill right through the holes in the aluminum gusset.
Cosmetics
As you can see in the photos above, it is common to have above-deck supports. But if you want to cover up the gusset, there are some options. You could encapsulate the gusset with outdoor carpet using contact adhesive. This is very easy with commonly-available aerosol adhesive from any hardware store. The outdoor carpet can be fitted to completely cover everything, even the bolt heads.
If you want the look of a full gusset , you could cut a triangle of treated wood under the gusset, and carpet the whole thing down to the swim deck floor.
Custom Installation on a 50--Foot Motor Yacht
One of our customers installed our Tilt-Up Rails on a 50-Foot Motor Yacht that did not have adequate swim deck support. So he adde both top and bottom support. Click here or on the picture to see several photos of his installation which will give you some ideas for your application.
Summary
As noted above, I would be glad to offer my feedback if you send me pictures of the top and underside of your swim platform and the framing where it connects to the outdrive ceiling area.
If you add one or two gussets to your boat, please take before-and-after photos and send them to me.
Send to sales@pwcrails.com
