New to me very old kayot pontoon boat with sterndrive OMC

kuleinc

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H!
Just bought a 50s or 60s Kayot pontoon boat. Its sits very low in the water, this is likely do to the steel pontoons and the custom engine pod with omc 2.5l and stern drive someone added some time...

Performance of the boat is only 12 MPH even though it has at least 120HP. When you push the boat to max RPM of 4300 it will go 12MPH, the bow comes up and the front 12 or 18 inches of the pontoons come out of the water completely! The back of the boat sinks down and the stern is I think actually touching or skimming the top of the water. The wake is like a tidal wave, it is HUGE for a pontoon boat, its a very big hump. I went to the bow while my wife was driving and looked under the boat, it looks like this is because the motor pod is v shaped on the front and is in the water. There is a TON of turbulence under the deck of the boat, the back half of the boat is engulfed in water spray, much worse than a normal pontoon boat. Its almost like a giant surfboard with a motor and propeller.

I know this thing is never going to be a fast boat, and that is fine. But I think it has a lot more potential than where it is currently at. I know nothing about hydrodynamics or pontoon performance. Should I add strakes? bow weight? a foil connecting engine pod to steel pontoons? The motor and stern drive I think are a stinger omc? I think the front mount of the engine might be manually adjustable therefore changing the trim of the stern drive? Should I play with this?

I got this for almost nothing and love its cute old school looks, just want to iron out the bugs of something someone may have done with the i/o omc setup... Once I get new tires and bearings on the trailer I can take it out of water and see just how far the motor pod hangs down compared to the pontoons. It seems like it has enough power to come up on plane, but doesn't because of so much weight in the back? It seriously lifts the front up and the stern down...
 

ahicks

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The steel pontoons would be a big deal here. Not only are they heavy, but at that age, I'd be surprised if there weren't some leaks. If there was water inside the tubes, it would easily create the picture you describe.

If the rest of the boat seems solid, I'd consider some new alum. tubes, and as they don't cost much extra, the new tubes would likely have strakes.

Before you do much from an investment standpoint, I'd have a pro look over the OMC gimble housing, U-joints, etc. No point in putting new tubes under a boat that's also up for expensive mechanical repairs. You could easily have a lot more invested in a boat that could have been replaced more economically.
 

Scott Danforth

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If it's an OMC stringer, no u-joints or gimble bearing.
 

ahicks

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Geez, fine. Don't bother having anyone look at it then......
 

HotTommy

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I don't know squat about your setup, but I can imagine two things that might cause the nose to rise as you describe. First, if there is water in the toons, on acceleration it would slosh to the back causing it to go lower and the water would stay there. Second, if the propeller is pointed upward (as when tilting an outboard up) that could drive the back end of the boat lower when under power. ... I agree with the advice to get a good handle on the situation before spending much money. This thing could nickle, dime and $100 you to death.
 

kuleinc

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Unfortunately I'll need to spend at least some money on the trailer to get it out of the water for inspection. The boats been in the water long enough for green hairs to grow on the pontoons at the water line, if it had holes wouldn't it have sunk by now?

The trailer needs four tires and four bearings, then I can pull it out and do some inspecting work. I can't see much of the omc stern drive because its so far under the boat, but I can see its silver, like the engine, and I can see the engine is not mounted to the transom. We went out in it again today, and you sort of get used to the speed, the speedometer does not work, and the motor just hums along, you almost forget you spent 45 minutes going 6 miles lol

I already know the boat will need a new deck this winter. If the pontoons are taking on water I'll start looking for aluminium ones and maybe an outboard motor to mount on the third new middle aluminium pontoon..

I think the motor could use a tune up, the wires and distributor cap look pretty old... But it runs pretty good so far! I just let the motor hum along at 3200 rpm, whatever speed that may be...
 

HotTommy

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If the toons are vented, they would likely have sunk if there were holes below the water line. But if the tanks are sealed, they would fill only to the level of the hole and leave air trapped above. . ... If you do take the boat out on a trailer, be prepared for the boat to be extra heavy IF it does have water in the toons.
 

kuleinc

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OK, here's the wake:


Front:


3/4 starboard view (canopy is from another boat):


Starboard side:


Stern:


Bow:


top:


Its an interesting boat. just found out the engine is 1985 vintage. I can't get to the stern drive to get the model off it, but once I get it out of water I can check its vintage. I think the boat is a 1959 Kayot Weekender, supposed to weigh 1260 pounds (with stock motor?) and have a capacity of 2350 pounds, much of which is probably taken up by the heavy i/o... Yes there is a bell on the front of the shade cover... it rings when the waves get a bit rough...
 
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ahicks

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Though I've been around my fair share of I/O's, that's a setup I haven't seen before. Kind of a mid-engine. Probably done like that for balance purposes.Usually, the I/O's set pretty low in the back. This one could make for an interesting project!
 

HotTommy

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any help on getting it to plane?
Either you've got a subtle sense of humor, or no one has told you about the difference between old pontoon boats and planing boats. Some newer pontoon boats have strakes attached to the logs that will allow them, with sufficient power, to rise up and plane sort of like planing boats. Pontoon boats without strakes do not rise up. They simply plow through the water. That is why older pontoon boats typically do not go as fast (with the same engine) as planing boats. They also typically use more fuel at typical cruising speeds.
 

kuleinc

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sounds like I need to buy a welder! I also ordered 4 tires for the trailer today! I'll check the bearings in it this weekend...
 

kuleinc

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So, we have been using boat to go around island and hang out on a beach. It does this fine. I think we would like to use it to tow a skier or wake board. I would like to get it up to 15 or 20 MPH. I also find the back of the boat is useless with the large motor pod. I'd like to convert the boat back to an outboard because of this. I'm thinking when I redo the deck this winter that would be the ideal time. How do I measure to tell how tall of an outboard I need? Is longer better so its in clean water? I also see two options for mounting outboard, a motor pod (cheap) and a third pontoon with built in pod. I realise it may be unorthodox to simply mount an aluminium center pontoon in between two steel ones, but would this help with speed? We had three adults, three small kids and some gear on board and if too many of us go to either end of boat, it dips into the water, I'm thinking third pontoon will help with this. Then I can replace two steel ones later...

OR should I just get a motor and pod, and mess with pontoons later? I'm also thinking 150-200 HP motor is in my budget...

Need some advice from some folks with experience here.
 

HotTommy

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I don't have time to offer an in-depth analysis of your plans, but here are some intial thoughts in no particular order.
1. If you start mixing steel and aluminum components, be aware of the problem of corrosion due to dissimilar metals.
2. If you buy a new engine pod or center log with engine pod, the height of the transom will be determined by the geometry of the new pod and how it attaches to your boat.
3. The common guidance is to have the anti-cavitation plate on your motor an inch or so below the lowest point on your engine pod. So the distance from the transom mount to the bottom of the engine pod is roughly what you'll want as the distance from the transom mount to the anticavitation plate on the engine.
4. You'll also want the anticavitation plate an inch or two below the water when underway, but if you hang a 400+ pound outboard way back on your boat, I suspect the rear will ride low and you'll have plenty of water for the prop.
5. A pontoon boat is about the simplest form of boat there is. It is two logs bolted together with metal cross bars. A marine grade plywood deck sits on top of the crossbars and you can arrange the fences, furniture and console anyway you like.
6. I took my old pontoon boat down to the basics before rebuilding it the way I wanted. I use it to tow tubes and skiers with a 115 HP outboard. Besure to attach the tow rope to something substantial like the logs, and not to the fence.
7. Before you invest in a 450# outboard, have three large people stand at the very back of the boat and see how it sits. You may want something lighter.

Good luck.
 

kuleinc

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Thats very helpful! I think one thing to consider here is the shape of my pontoons, they do not look like any other pontoon I have seen. They taper in the back like a cone and so offer even less float than current logs with their flat backs. Any guidelines on how much horse power I need on a 24 foot boat that is 8 feet wide? What about if I really can get a 200 horse power engine on the back of it, what kind of structural advice can you give? I'm sure it never had any kind of substantial motor on the back...
 

kuleinc

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I should also note that the back of the motor cover box, which is also the transom is about 5 feet from the back of the boat. This houses a 2.5L chevy vega motor from 1985, which I'm sure is iron, and very heavy, not to mention the electric shift OMC stringer mount stern drive hanging on the outside of the transom. This is all enclose in an aluminium box, and the 15 gallon gas tank is right in front of the engine. As it sits now with my 200 pounds on either end measuring, the back of the deck is 6 inches out of the water and the front is 10 inches out of the water. As soon as I get the new tires and wheel bearings and bunk carpet on the trailer I can pull the boat out of the water and measure the steel pontoons. The box the motor is in is always in the water, and breaks the the water between the pontoons, so the huge turbulence cannot escape from under the boat like on a twin pontoon boat. The front of the motor box does come to a point a foot or two infront of the wooden box seen above deck, but it must create a HUGE amount of drag. So much drag the water escapes over the pontoons and vents between them and the deck... Its almost like there are two pontoons and then the back end of them is attached in the water...
 

HotTommy

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We shot this video of my neice skiing behind my 24' pontoon boat last weekend. I estimate we had 1,000# of people and equipment on board. We were going about 18-19 MPH at 4800 RPM on my 115 HP Mercury four cycle engine. Full throttle would likely have yielded 22 MPH. She is not a big person, but I have also towed her 230# husband. .... My point is that you don't need 200 HP to ski. .... There are significant issues to be addressed if you hang a 200 HP motor on your boat. Plainly the logs and crossbar structure has to be strong enough to withstand the downward weight on the back and both the forward push and the can opener like twist of the engine on the transom/boat. In addition, since I assume your motive is to go fast, you will be putting wind loads the boat was not design to see on the fence and top. Know that the force of the wind increases as the square of its speed. So a boat going 45 MPH is experiencing 9 times as much wind blast as one going 15 MPH.

My goal here is to be helpful without telling you what to do with your project. But I admit that I am not entirely certain what you are wanting to do. You bought a very old boat whose primary asset was, IMHO, it's cute uniqueness. I assume it didn't cost a lot and that was also part of its appeal. .... You express willingness to spend a lot more on it in both time and money to turn it into a more conventional, modern pontoon boat that goes fast. If that was your goal, I don't understand why you started with such a challenging old boat. .... If you throw enough time and money at a project, you can do almost anything. But in my experience, every project costs twice as much and takes three times as long as the most realistic estimate.
 
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ahicks

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I'll be more blunt about it. You have a really unique neat boat - BUT - it was not designed to go fast. If you want to go fast(er), you'll be way further ahead starting over again with a different boat.

BTW, the Vega engines are alum. The engine you have, if it's a 4 banger, is far more likely known as the "Iron Duke", which was a popular GM 4cyl. engine used in something like the early Nova's. There were a TON of them used in Mercruiser and OMC 120 and 140 hp stern drives.
 

kuleinc

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Been searching and searching, finally found an article that mentions the OMC 120 hp outdrive weighs 600 pounds! Also no need to be blunt, I understand what you said. I also have a VW vanagon westy with a 220 hp 1.8t engine in it that I put together :) I'm seriously considering something like a mercury 150HP elpt outboard, or something similar with 200 hp...

Does anyone have any experience with the american pontoon company? They make pontoons with a buoyant outboard mount and built in fuel tank! usapontoon.com
 
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