SWIMPLATFORM EXTENTIONS

 

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           SWIMPLATFORM EXTENTIONS

It is popular now a days to modify our boats and add the accessories that we see on new boats, to change the issues that older boats were plaiged with in the 80s and 90s. Boat owners are doing things as simple as changing to LED lights right through to adding oversize swim platform extensions and everything in between. Trying to create a more up to date and usable boat, is this a good idea? Will these type of modification affect the performance of the boat (both mechanical and ride performance). I have operated a few boats where the addition of accessories had completely destroyed the performance of the boat. Unfortunately it always seems to be the first time boat buyer who ends up owning these boats, the seller knows the boat is no longer performing but the new boater has nothing to compare the boat to and assumes the ride is natural.

What are the problems associated with installing accessories like swim plat forms, radar arches, generators, extra batteries and other weight and load changing items to our boats. All boats that come to market are designed with several important standards and measurements in mind, these include floatation, center of gravity and load weight balance. The boats are engineered and weighed with full loads this includes fuel, fresh water, batteries all of the systems that the boat was designed to have and use from the factory. Changes to any of these measurements will change the way the boat handles and performs.

 By adding weight you affect the way the boat sits in the water when at the dock. This can include a list to one side, a drop in the water line (aft, forward or over all). These change can and will affect exhaust flow, safe height for thru hull locations from the water line, proper operation of bilge pumps, and of course the ability for floatation that the manufacturer installs to work correctly or at all. In the case of a list many boaters try to counter act it by adding more dead weight to the high side making the situation worse. The moment that you have changed the load enough to create a change at the water line you have changed the way the boat will perform. Keeping in mind I have not allowed for all your personal items you keep on the boat and for some boaters this can be the equivilent of a pick up truck load of items of all shapes, weight and description.

  Lets go over the main items we add to our boats now a days to make them more up to date:

Swim platform extension: The first question you need to ask is did my boat come with this option what was the size and how was it mounted. Am I running the correct engine package combination to accept this accessory. Quite often the boat you have did not have the platform added at the factory due to the fact that the boat has V6 power rather than V8 power or you may have a single engine rather than a twin engine combination. Possibly the boat came optioned with a bundle of accessories that you don't have and this could include counter weight items that are moved forward such as a generator in front of the motors to offset a heavier transom load. If you are planning to add a platform to a boat that did not come with this option here are the things you need to consider.

• What is a reasonable size. You may want a patio back there but can you see it from the helm, how much extra in slip fees will this cost you as you are changing the length over all. What are you really using the swim platform for, is it just to make boarding the boat easier and are you looking to mount a BBQ. How will this change the way I tie my boat up during bad weather
  
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• How much does it weigh. Load weight right on the transom is one of the evasive changes to a boat you can make. The reason for this is you are directly affecting the center of gravity. This will change the way the boat planes, the affect of the trim tabs and drive trim. The depth of water the drives are in at the dock, and the exhaust flow. If you have thru hull exhaust you can sink the ports under the water completely or only part way either is not a good thing. this can increase the back pressure on the motor, and possibly leave the mufflers full of water at all times. In the case of and inboard out board it will change the height of the exhaust water in the bull horn ( the exhaust outlet at the back of the motor) outing stress on the flapper valves and increasing the opportunity to hydrolic the motor on shut down or while backing up. Both of these situations are expensive to repair and can blow a motor.  

• How will the hull run after. A swim platform can create several bad situations if it is not designed to match the boat correctly. If the platform is mounted down low two important effects can happen. the first is suction this is when the bow of the boat starts to lift and the platform is right down in or at the surface of the water, this creates a vacuum effect were the boat has to power past and pull the platform out of the water. When this happens the boat lays bow up for way to long and with out enough power will not plane at all. The second is the following sea scenario were the platform act like a trim tab and lifts the back of the boat out of the water. As the waves roll up behind they get under the platform and have no were to break so it just lifts the boat up and can create a situation were you can no longer control the boats direction. This same situation will show itself while trying to back down or if you are floating or at anchor. The boat can actually come right around on you and you will be facing the direction you were coming from in a second!
  

• What will it be mounted to. There are three ways to mount an extension, over the platform, under the platform or directly to the transom. Most over platforms mount this way to prevent the trim tab effect, the silly part of this is the platform is useless as the platform sits a foot or more out of the water. they look more like a back deck than a swim platform. The second is under mount this is generally how the factory installs platform extensions. it is clean neat and functional, But you need to restrict the size try to stay close to the factories sizes any more and you will probably find it floating past you one day. You must be sure that all the interior support structure is in the boat to do this as the bolts go up through the bottom of the platform hull area. Just because the boat was designed for this does not mean that the support structure is in the boat. The third is way is to mount right to the boat transom, picking the right height and being sure that the structure of the transom is solid is important. You do not want to half ass this mounting set up. Quite often there are issues with this set up as a larger platform will require different bolt patterns and support bars. Check the engine compartment first you may have steering bars, pumps, or your motors may be so close that placing support bars were they need to be maybe impossible. Try to remember that in some cases the reason for the factory installing small platforms is an engineering issue not just due to the fact that they were not wanting to do more.

• What do you want the extension for. If you want a functioning platform than you probably will not like the over mount platform at all, the platform can be unusable for swimming and re boarding. This falls into a safety issue as well if you have high decks or deck sides you need to be able to get down to the water in the case of an accident. It would be ridiculous to attempt to get a hurt person up more than a foot out of the water on this type of platform. In some cases that the re boarding issue, if you feel over board was the only reason the factory put any platform at all on the boat. Not all accessories were created for there good looks they just had to function. If you are just trying to add length seriously sell the boat and buy a bigger one.

Just do not assume that the extension you buy or have built will work you need to consider a lot of things before you slap three feet of floor on the back of your boat!   It can turn out fantastic or be the biggest failure and destroy the performance characteristics of a great boat.

Davit Systems fall under the same rules as adding a platform they are both transom load weight additions. You must make the same considerations to the boat in either case, The difference with a davit system is that you can calculate the weight load and have a marine engineer or the manufacturer inform you of its feasibility and the effects of the weight. If you buy a boat with a davit system be sure you find out the recommended load before you just load your sea doo or tender.

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