I need to add a outboard motor mount to the transom of a 1974 Catalina 27. It is not cored , and the fiberglass is very thin. How should I mount the outboard, and what type of reinforcement will I need to do. It surely doesn't feel like that fiberglass will hold the 100 or so pounds the engine weighs. There is no motor well in the boat, the old a-4 was taken out.
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Outboard?
Why? Why install an outboard on the transom? The boat will perform better under sail and under power with an inboard. The boat was designed for an inboard. It will be easier to put a new engine where the good old A4 was than to hack the boat up to hang an outboard off the transom. Why?
Why? Why install an outboard on the transom? The boat will perform better under sail and under power with an inboard. The boat was designed for an inboard. It will be easier to put a new engine where the good old A4 was than to hack the boat up to hang an outboard off the transom. Why?
Cost
Cost & ease of maintance. I can spend $2,500.00 for a brand new Nissan 9.8 hp, with cockpit controls. It would cost way more to replace the old inboard , and way more in labor.
Cost & ease of maintance. I can spend $2,500.00 for a brand new Nissan 9.8 hp, with cockpit controls. It would cost way more to replace the old inboard , and way more in labor.
Reinforce the transom
My father bought a "run-about" power boat, 18 footer, a long time ago. When he got it home he realized the transom had some rotten parts to it. He back the transom with marine plywood, then glassed over the whole thing. Recently I had my rectangular hole in the back of the transom glassed in; as reinforcement, the chap also used marine plywood as backing, the plywood and back of transom was further glassed in. Now that area holds a power bracket - up or down at the push of a button - with a Merc 9.9 Big foot. The boat is a 1975 Catalina 27. Merry Xmas
My father bought a "run-about" power boat, 18 footer, a long time ago. When he got it home he realized the transom had some rotten parts to it. He back the transom with marine plywood, then glassed over the whole thing. Recently I had my rectangular hole in the back of the transom glassed in; as reinforcement, the chap also used marine plywood as backing, the plywood and back of transom was further glassed in. Now that area holds a power bracket - up or down at the push of a button - with a Merc 9.9 Big foot. The boat is a 1975 Catalina 27. Merry Xmas
Cheaper?
I hope you never have to use the motor on anything but calm days. I hope you don't have a battery to charge. I hope you don't mind killing the resale value of your boat. The C27's that were built for OB power don't hang the OB off the transom. There's a reason. Transom mounted OB's put weight where you don't want it, either when motoring in waves or sailing. Transom mounted OB's pull the prop out of the water when motoring in rough weather, inboards do not. Inboards have real alternators, how are you going to charge the batteries? Your 9.8 HP Nissan has a 6 amp alternator, just big enough to keep the starting battery charged. If you have only one 100ah battery for the house bank and start to charge at 50% discharge, your 9.8 Nissan has to run for almost 10 hours to charge the battery. And that's assuming that it has a voltage regulator that will put out 6A for 10 hours. A 15-20 hp diesel will spin a 75A alternator and charge your battery in less than 1 hour. The inboard diesel will sip fuel rather than gulp it. Your fuel usage will be less than 1/2 of the OB. With the OB you also get 6 gallon portable tanks unless you use the gas tank that is inside the boat. Will the OB draw fuel that far? When you go to sell the boat, the new owner will want/need a survey to get insurance. Will your DIY transom mount OB pass a survey? If not, you can't give the boat away. Now how much money have you "saved"?
I hope you never have to use the motor on anything but calm days. I hope you don't have a battery to charge. I hope you don't mind killing the resale value of your boat. The C27's that were built for OB power don't hang the OB off the transom. There's a reason. Transom mounted OB's put weight where you don't want it, either when motoring in waves or sailing. Transom mounted OB's pull the prop out of the water when motoring in rough weather, inboards do not. Inboards have real alternators, how are you going to charge the batteries? Your 9.8 HP Nissan has a 6 amp alternator, just big enough to keep the starting battery charged. If you have only one 100ah battery for the house bank and start to charge at 50% discharge, your 9.8 Nissan has to run for almost 10 hours to charge the battery. And that's assuming that it has a voltage regulator that will put out 6A for 10 hours. A 15-20 hp diesel will spin a 75A alternator and charge your battery in less than 1 hour. The inboard diesel will sip fuel rather than gulp it. Your fuel usage will be less than 1/2 of the OB. With the OB you also get 6 gallon portable tanks unless you use the gas tank that is inside the boat. Will the OB draw fuel that far? When you go to sell the boat, the new owner will want/need a survey to get insurance. Will your DIY transom mount OB pass a survey? If not, you can't give the boat away. Now how much money have you "saved"?
JUST NEED MOUNTING ADVICE / NOT DEBATE
Thanks Moody, the name seems to fit. I've already made up my mind to mount the outboard, I'm just looking for a little help on HOW to do it. I'm not looking to debate the merits of inboard vs. outboard. If anyone has any suggestions on how to mount & reinforce the bracket, I would appreciate your comments.
Thanks Moody, the name seems to fit. I've already made up my mind to mount the outboard, I'm just looking for a little help on HOW to do it. I'm not looking to debate the merits of inboard vs. outboard. If anyone has any suggestions on how to mount & reinforce the bracket, I would appreciate your comments.
Access is the key.
I would think if you have access to the inside of the transom, you could put some half inch plywood or thinner metal backing plates inside the transom to be safe, and just drill holes and bolt on the motor mount. The bigger the better on the backing plates to spread the load. My old C25 did fine with the factory installed motor mount. I don't think the C27 transom is any weaker than the C27. If you think the C27 transom is substantially weaker, you could maximize the backing plate, and glass it in, but big backing plates will always help. The closer you can center the mount, the better. But you can mount it off center if you have to and just angle the motor slightly to compensate. Determining the height of the motor mount is important to get enough depth, without flooding the power head. Even with an adjustable mount. I have to agree with Moody, that in rough conditions, the motor popping out of the water was a B*%$. That’s why I always sailed when it got rough.
I would think if you have access to the inside of the transom, you could put some half inch plywood or thinner metal backing plates inside the transom to be safe, and just drill holes and bolt on the motor mount. The bigger the better on the backing plates to spread the load. My old C25 did fine with the factory installed motor mount. I don't think the C27 transom is any weaker than the C27. If you think the C27 transom is substantially weaker, you could maximize the backing plate, and glass it in, but big backing plates will always help. The closer you can center the mount, the better. But you can mount it off center if you have to and just angle the motor slightly to compensate. Determining the height of the motor mount is important to get enough depth, without flooding the power head. Even with an adjustable mount. I have to agree with Moody, that in rough conditions, the motor popping out of the water was a B*%$. That’s why I always sailed when it got rough.
OK ...
Here's how I'd do it. Take the bolt pattern of your OB mount and find the area of the mount base at the transom. Make two motorboard pads out of 3/4" ply. One twice the area of the mount, and the second one 4 times the area of the mount. The large one goes inside the transom and the smaller one on top of the first one. Sand/grind the inside of the transom to clean the surface and expose the fibre-glass. Shape the first doubler to fit the curve of the transom, doesn't have to be super close, 1/8" gaps are ok. Get some heavy FG mat to act as a pad between the transom and the first doubler (the mat will fill any gaps). Drill the holes for the motor mount through the transom and the two motor boards so the mount is centred on the doubler's. Do a couple of dry runs to make sure it all fits. Make sure the mounting bolts are long enough to go through the transom, both boards and leave an inch or so for washers and nuts. When you are happy with the fit, mix up a batch of epoxy. Coat the inside of the transom and both sides and all edges of both motor boards. Let the epoxy set for 12-24 hours. Cut the mat to fit the large board, two or three layers would be good. Use some temporary bolts (spray the bolts with PAM so the epoxy won't stick to them) to locate holes in the mat and wet the mat out with epoxy, one layer at a time. Take the large board with the mat and install it inside the transom while the epoxy is still liquid. Use the bolts to clamp the board to the transom (a bunch of epoxy should ooze out from the mat). After the epoxy sets, remove the bolts. Coat the back of the large motor board with another coat of epoxy and glue the small board on. If the small board doesn't fit flat on the first board add some mat between the two. Respray the bolts with PAM and use them for clamps. After the epoxy sets, you have all the load from the motor spread out over a large area of the transom and a solid laminate that shouldn't stress the transom/hull joint. To finish it off, I'd add thickened epoxy fillets all around both boards and 2-3 layers of medium to heavy FG cloth over the whole thing. Run the first layer about 3" past the edge of the boards, and 3" more on each layer after. The idea is to prevent any point loads that could crack the transom. Catalina's are built pretty heavy, I'd guess the transom is about 1/4" thick if not more. You might be able to use 1/2" ply instead of 3/4". No need to use marine grade plywood, since the mount won't be underwater and all the wood will be sealed in epoxy. Exterior A-B should be fine. As a point of reference, the transom of the runabout I'm building has a 1 1/2" (2 layers of 3/4") thick motorboard and it has a 15HP motor and weighs about 200#. The loads on the transom of your C-27 will be higher when the motor is tilted up and the boat goes through waves. I'm glad to help, I just wanted to point out some of the trade-offs when you replace an inboard with outboard power.
Here's how I'd do it. Take the bolt pattern of your OB mount and find the area of the mount base at the transom. Make two motorboard pads out of 3/4" ply. One twice the area of the mount, and the second one 4 times the area of the mount. The large one goes inside the transom and the smaller one on top of the first one. Sand/grind the inside of the transom to clean the surface and expose the fibre-glass. Shape the first doubler to fit the curve of the transom, doesn't have to be super close, 1/8" gaps are ok. Get some heavy FG mat to act as a pad between the transom and the first doubler (the mat will fill any gaps). Drill the holes for the motor mount through the transom and the two motor boards so the mount is centred on the doubler's. Do a couple of dry runs to make sure it all fits. Make sure the mounting bolts are long enough to go through the transom, both boards and leave an inch or so for washers and nuts. When you are happy with the fit, mix up a batch of epoxy. Coat the inside of the transom and both sides and all edges of both motor boards. Let the epoxy set for 12-24 hours. Cut the mat to fit the large board, two or three layers would be good. Use some temporary bolts (spray the bolts with PAM so the epoxy won't stick to them) to locate holes in the mat and wet the mat out with epoxy, one layer at a time. Take the large board with the mat and install it inside the transom while the epoxy is still liquid. Use the bolts to clamp the board to the transom (a bunch of epoxy should ooze out from the mat). After the epoxy sets, remove the bolts. Coat the back of the large motor board with another coat of epoxy and glue the small board on. If the small board doesn't fit flat on the first board add some mat between the two. Respray the bolts with PAM and use them for clamps. After the epoxy sets, you have all the load from the motor spread out over a large area of the transom and a solid laminate that shouldn't stress the transom/hull joint. To finish it off, I'd add thickened epoxy fillets all around both boards and 2-3 layers of medium to heavy FG cloth over the whole thing. Run the first layer about 3" past the edge of the boards, and 3" more on each layer after. The idea is to prevent any point loads that could crack the transom. Catalina's are built pretty heavy, I'd guess the transom is about 1/4" thick if not more. You might be able to use 1/2" ply instead of 3/4". No need to use marine grade plywood, since the mount won't be underwater and all the wood will be sealed in epoxy. Exterior A-B should be fine. As a point of reference, the transom of the runabout I'm building has a 1 1/2" (2 layers of 3/4") thick motorboard and it has a 15HP motor and weighs about 200#. The loads on the transom of your C-27 will be higher when the motor is tilted up and the boat goes through waves. I'm glad to help, I just wanted to point out some of the trade-offs when you replace an inboard with outboard power.
Thanks Moody
Thanks Moody, I appreciate your help and will follow it. Also, do you think I should use any horizontal type of support from the plywood to the bulkhead by the rudder? I was thinking about doing this to control any flex from the transom?? Thanks again.
Thanks Moody, I appreciate your help and will follow it. Also, do you think I should use any horizontal type of support from the plywood to the bulkhead by the rudder? I was thinking about doing this to control any flex from the transom?? Thanks again.
Two Thoughts
The 1986 C27 that I owned came stock from the factory with an externally mounted outboard. The mount was braced internally with both a plywood "doubler" and a metal plate inside the transom. It was mounted offset to the port side of the boat. Didn't make any difference in the boats tracking, and avoided potential motor interference with the rudder, and allowed the fold down boarding ladder to remain useful. Two of the clear advantages of the outboard in this configuration were that it could be lifted and tilted clear of the water on both tacks - no drag from the motor & prop = faster boat, and the enormous storage locker available under the cockpit where the inboard engine and fuel tank would have been installed. Locking down the steering of the outboard, electric start and adding a remote shift/throttle kit rounded out the installation. As mentioned, the outbooard had minimal charging capabilities, but the trade off of just hauling it into the shop for service made it all worthwhile for me. The two downsides that I experienced were propulsion in reverese was terrible - I just learned to live without using reverse - and I think I came out a better boat driver because of it. We also got into a couple of situations in short choppy water where the boat was hobby-horsing up and down - motor down in the water, motor up out of the water. Obviously we lived, and an inboard would have made it a little less stressfull, but I still stick with the postion that the outboard on the C27 was a good choice. Good Luck! Tim Brogan April IV C350 #68 (Was Inamorata C27 #6111) Seattle
The 1986 C27 that I owned came stock from the factory with an externally mounted outboard. The mount was braced internally with both a plywood "doubler" and a metal plate inside the transom. It was mounted offset to the port side of the boat. Didn't make any difference in the boats tracking, and avoided potential motor interference with the rudder, and allowed the fold down boarding ladder to remain useful. Two of the clear advantages of the outboard in this configuration were that it could be lifted and tilted clear of the water on both tacks - no drag from the motor & prop = faster boat, and the enormous storage locker available under the cockpit where the inboard engine and fuel tank would have been installed. Locking down the steering of the outboard, electric start and adding a remote shift/throttle kit rounded out the installation. As mentioned, the outbooard had minimal charging capabilities, but the trade off of just hauling it into the shop for service made it all worthwhile for me. The two downsides that I experienced were propulsion in reverese was terrible - I just learned to live without using reverse - and I think I came out a better boat driver because of it. We also got into a couple of situations in short choppy water where the boat was hobby-horsing up and down - motor down in the water, motor up out of the water. Obviously we lived, and an inboard would have made it a little less stressfull, but I still stick with the postion that the outboard on the C27 was a good choice. Good Luck! Tim Brogan April IV C350 #68 (Was Inamorata C27 #6111) Seattle
Not sure ...
I'm not sure that you will need a brace from the transom to the rudder post area. I'm not real clear in my mind what the construction is like back there. You will probably have to offset the motor to one side a bit for rudder clearance. Try flexing the transom where the mount will go. I don't think there will be a problem if the motor load is spread over a large area of the transom. The transom<>hull joint should handle all the loads just fine (it has to handle rig loads form the backstay). If it would be handy to partition the aft locker, run a bulkhead from between the motor support and the cockpit inside the locker. By the time you're done you would probably be able to hoist the boat out of the water by the motor mount.
I'm not sure that you will need a brace from the transom to the rudder post area. I'm not real clear in my mind what the construction is like back there. You will probably have to offset the motor to one side a bit for rudder clearance. Try flexing the transom where the mount will go. I don't think there will be a problem if the motor load is spread over a large area of the transom. The transom<>hull joint should handle all the loads just fine (it has to handle rig loads form the backstay). If it would be handy to partition the aft locker, run a bulkhead from between the motor support and the cockpit inside the locker. By the time you're done you would probably be able to hoist the boat out of the water by the motor mount.
Works Well
Aaron, I lost my Catalina 27, 1974 TM in Katrina. When I say lost, not even a splinter found so far. I did have an Evinrude 9.9 Yachtwin hung on the back. It worked without any problems. When motoring in heavy seas (had to go directly into the wind now and then)the prop did occasionally come out, but it was never a problem. I am inclosing three photos. One here and others in follow up replies. The mount was older and not a problem to pull up. A little WD40 or SailKote helped. When up and tilted, the 9.9 long shaft was out of the water and no drag. As you will see, it was mounted dead center and did not interfere with the rudder when in operation. I had cockpit controls, on/off, f/n/r. Reverse worked well if you gave it enough gas to have maneuvering speed. First photo on the hard doing a little flushing. You can see how deep the long shaft goes and that it is not a problem with the rudder. There were two circular cuts in the transom, one for the fuel line and one for the electrical and engine cable connections. You will see this better in another photo.
Aaron, I lost my Catalina 27, 1974 TM in Katrina. When I say lost, not even a splinter found so far. I did have an Evinrude 9.9 Yachtwin hung on the back. It worked without any problems. When motoring in heavy seas (had to go directly into the wind now and then)the prop did occasionally come out, but it was never a problem. I am inclosing three photos. One here and others in follow up replies. The mount was older and not a problem to pull up. A little WD40 or SailKote helped. When up and tilted, the 9.9 long shaft was out of the water and no drag. As you will see, it was mounted dead center and did not interfere with the rudder when in operation. I had cockpit controls, on/off, f/n/r. Reverse worked well if you gave it enough gas to have maneuvering speed. First photo on the hard doing a little flushing. You can see how deep the long shaft goes and that it is not a problem with the rudder. There were two circular cuts in the transom, one for the fuel line and one for the electrical and engine cable connections. You will see this better in another photo.
Inside the transom
Aaron, This is the inside of the transom locker. As you can see, good place for fuel and other non flammable necessities. You can see the cutaway and placement of what appeared to me to be about 1/2 to 3/4 heavy marine plastic as a support between the outer and inner rear transom structure. The only things I would have done differently would be to have larger backing plates for the four mounting screws. And I would have used shorter screws and placed acorn covers on the ends.
Aaron, This is the inside of the transom locker. As you can see, good place for fuel and other non flammable necessities. You can see the cutaway and placement of what appeared to me to be about 1/2 to 3/4 heavy marine plastic as a support between the outer and inner rear transom structure. The only things I would have done differently would be to have larger backing plates for the four mounting screws. And I would have used shorter screws and placed acorn covers on the ends.
GREAT PICTURES
Randy, First off, I'm sorry to hear about your boat. I hope you get back into one soon. Second, thanks for the pictures. Exactly what I needed to see. I will incorparate moodys suggestions, and I'm sure it will work out great. Thanks for all your replies.
Randy, First off, I'm sorry to hear about your boat. I hope you get back into one soon. Second, thanks for the pictures. Exactly what I needed to see. I will incorparate moodys suggestions, and I'm sure it will work out great. Thanks for all your replies.
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