Starcraft chieftain i/o to outboard conversion

[Hofty]

Folks,

I have been doing a lot of reading on the topic but come to a realization that perhaps I'm overthinking the topic.

Currently the boat has a Volvo B20 with Aquamatic 100 stern drive. The magical fact here is that it appears the motor weight is placed on the transom via the transom shield and flywheel cover. Yes!!!! No engine mounts and this has been the setup on this boat from day 1. The transom takes the full load of power and its not transferred to engine mounts

Most forums state that an i/o transom setup was not meant for an outboard to sit on the transom. The engine power distribution shifts the weights to the engine mounts and stringers. I would agree that slapping an outboard on would severely impact a transom for one not designed for the power being against the transom.

In my case. No engine mounts and the power being transferred by the stern drive right to the transom, does this signify that I can fill the keyhole properly and install a single offshore bracket to the transom with perhaps some transom reinforcements and get away with a pod on the rear of the boat?

See attached pictures of the engine when I received the boat for a better understanding. Trying to get away with this project without extensive costs but also doing it properly.

Any advice is appreciated.

 

[matt167]

If you want cheaper. Chopping out the transom keyhole larger and sliding in a donor boats 3.0l mercruiser would be the quickest, cheapest way. StarCraft used a 4x4 for the front mount when they setup mercruiser 2.5 and 3.0.

For a pod, it ties into the transom structure for support and then it has to provide flotation and support for a 400# plus engine, that will be leveraged farther out on the transom on the other side than the load it was designed for. Think about it. The pod will push the motor back ~ 2 feet so that the motor can turn fully without hitting the transom. That 2 feet is like a breaker bar on your cars lug nuts but the force is on the transom.. you need to make sure the load transfers through the center of the boat…. The 400# came from the weigh of a 125 Merc 2+2 which is like 415# from memory which really isn’t enough with a pod

 

[racerone]

Wood in the transom looks like it might be rotten.

 

[airshot]

Replace the transom wood with something more heavy duty and add some supports to those stringers which appear to be aluminum. Should not be hard to Fab some nice HD gussets to go from stringers up the transom. Then add your pod or other mount for an outboard. Replace the exterior plate with one that helps support the new motor mount. I would go with a nice two stroke to match the period of the boat. Don't see an issue if your fab skills are good...

 

[Hofty]

The feedback has been great. So essentially I can tie the transom into the stringers via gussets and a large steel plate on the inside of the transom to ensure the weight on the transom is transferred to the hull/stringers like in the attached pictures? Essentially a perfect project to cut some steel and perhaps hire a local welder to reinforce the area where I tie in?

 

[matt167]

You don’t want steel. Use aluminum and wood. Build knees that bolt or rivit to the stringers and build a support system. You can buy ready made pods designed by marine architects

 

[havoc_squad]

If you go the outboard Conversion route, make sure you go with a company that makes those conversion brackets to the correct specs of your boat, including the center of gravity of the boat.

Last thing you want is installing one that alters the boat balance too much while under way and cannot reach planing speeds because the bow digs in the water too much or is too stern heavy with too little bouyancy on the outboard bracket/stern.

Those brackets drastically alter the boat's weight balance with the bracket acting as a lever with the weight of the outboard.

 

[dingbat]

1979 Starcraft Islander. I/0 to outboard conversion.

A bit of back ground history. Over the years I have had at least one boat kicking around.Many years ago I had a smaller boat rigged up for fishing Erie. In those days pickerel fishing in Erie was second to none. The hull was to short at 15 ft but several friends and I had a lot of fun. Even the...

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