Transom replacement, curved to straight question

[bikerider]

I have a 12 ft Starcraft that I will be replacing the transom on hopefully this coming winter. The transom dips down a bit from edges to center about 1 1/4" (see pictures). Is there any reason I can't make it level with the back edges of the boat when I replace it? I have a 5hp outboard on it currently. I measured, and if I did make the new transom level, the outboard's cavitation plate would be about level with the bottom of the hull. Currently the cavitation plate sits a bit lower than the bottom of the hull. Is there any reason I shouldn't make the transom level across the back when I replace it?

(The pictures are of the same model Starcraft, but not my actual boat)

 

[Crazyboat]

It's set that way to accommodate a short shaft outboard. If you go straight across your outboard will sit too high and you'll have performance issues galore. At least that's how I see it. If going straight across is easier, do so but cut out a notch where the engine will sit.

From what I see, the aluminum looks in good shape, if just replacing the wood, use the old as a template. Or do you plan on removing and replacing the entire transom?

 

[LDUBS]

Another reason. By keeping the dip you can reuse the existing top cap.

 

[jethro]

Ideally you want the cav plate a bit lower, but then again, it's just a 5hp so it's not like you are going to really be on plane so it may not be a big deal. If it were me I would replicate what is there exactly. Plus, how would you fabricate a new top cap? oop, I see LDUBS beat me to that.

 

[bikerider]

It's set that way to accommodate a short shaft outboard. If you go straight across your outboard will sit too high and you'll have performance issues galore. At least that's how I see it. If going straight across is easier, do so but cut out a notch where the engine will sit.

From what I see, the aluminum looks in good shape, if just replacing the wood, use the old as a template. Or do you plan on removing and replacing the entire transom?

The pictures in my first post are of the same model Starcraft, not my actual boat. I took measurements and if I made the transom straight across, the outboard's cavitation plate will still sit lower than the bottom of the hull. The cap on mine is broken, so I need to replace the wood and top cap.

 

[bikerider]

Another reason. By keeping the dip you can reuse the existing top cap.

I forgot to mention in my first post that my top cap is broken and needs to be replaced. I don't know where I could source that if the transom was changed to straight across.

 

[bikerider]

Ideally you want the cav plate a bit lower, but then again, it's just a 5hp so it's not like you are going to really be on plane so it may not be a big deal. If it were me I would replicate what is there exactly. Plus, how would you fabricate a new top cap? oop, I see LDUBS beat me to that.

I took some measurements, and the cavitation plate would still sit lower than the bottom of the hull if the transom were straight across the back. I don't know where I would find a plate for the top if the design were changed. I'm asking questions now so I can be prepared and know what to do when the time comes to replace it.

 

[LDUBS]

I forgot to mention in my first post that my top cap is broken and needs to be replaced. I don't know where I could source that if the transom was changed to straight across.

Aw shoot. That is too bad. I forgot these pic's weren't your actual boat. Sorry about that.

If I had to source one, I would take the old one to a metal fabricator and ask how much to fix it or make a new one.

Back to the main question, I would leave the transom as is. Like @jethro says, it is a 5HP. How much difference is this fine tuning going to make.

 

[LaqueRatt]

In your shoes, I might go straight across too. Sounds like the motor will be close to where it needs to be anyhow and you can make a new top cap yourself out of a piece of square tubing of the correct size. Just cut/grind one side off and drop it right on. I do a bit of metal fabbing and duplicating that gentle curve I think would involve using a massive press like they use for stamping body panels for cars.

 

[bikerider]

In your shoes, I might go straight across too. Sounds like the motor will be close to where it needs to be anyhow and you can make a new top cap yourself out of a piece of square tubing of the correct size. Just cut/grind one side off and drop it right on. I do a bit of metal fabbing and duplicating that gentle curve I think would involve using a massive press like they use for stamping body panels for cars.

I may have to use rectangular tubing (if there is such a thing) to make sure all the new transom wood is covered on the backside of the boat.

 

[LaqueRatt]

Sounds like welding may be involved if that's what you want to do. I've never seen rectangular tube stock, just square and round. It may exist though.

You could always bend two lengths into Ls and overlap on top. Maybe with the right tools you could bend a U, but don't think I could with my brake. It's just too narrow.

 

[LDUBS]

Rectangular aluminum tubing is out there but the stock sizes seem pretty limited (like 1.5" or 2" wide). The 2" wide with 1/8 walls would have an inside width of 1.75".

 

[lckstckn2smknbrls]

Rectangular aluminum tubing is out there but the stock sizes seem pretty limited (like 1.5" or 2" wide). The 2" wide with 1/8 walls would have an inside width of 1.75".

You could put an 1/8" spacer on the inside.

 

[LDUBS]

You could put an 1/8" spacer on the inside.

Add in the thickness of the transom skin and that would get it pretty close.

 

[Still Afloat]

I may have to use rectangular tubing (if there is such a thing) to make sure all the new transom wood is covered on the backside of the boat.

You could go with rectangular tube or architectural channel which has flat sides and squared inside corners. Structural channel has tapered inside walls for strength but, it may not fit well as a cap. Similar to rectangular tubing, uneven legs are available. For example, 1.5” wide with 1” legs or 2 x 1.5, etc. Dimensions are measured on the outside so you will need to subtract the wall thickness for the inner dimensions.

 

[bikerider]

You could go with rectangular tube or architectural channel which has flat sides and squared inside corners. Structural channel has tapered inside walls for strength but, it may not fit well as a cap. Similar to rectangular tubing, uneven legs are available. For example, 1.5” wide with 1” legs or 2 x 1.5, etc. Dimensions are measured on the outside so you will need to subtract the wall thickness for the inner dimensions.

Thanks for the info. I didn't know about that.

 

[bikerider]

It looks like I have more things to look into. I appreciate everyone's input. It seems like the top cap has more to do with being a finish than really making the transom sturdy. Is that a correct assumption?

 

[LDUBS]

It looks like I have more things to look into. I appreciate everyone's input. It seems like the top cap has more to do with being a finish than really making the transom sturdy. Is that a correct assumption?

Protects the transom from water incursion.

 

[LaqueRatt]

I have a boat with no cap on it. Doesn't seem to be a problem. Looks a bit unfinished though.

 

[bikerider]

Protects the transom from water incursion.

Most of the transom replacements I've seen are two pieces of marine plywood sandwiched together so I guess the top cap is kind of important.