Been fiddling with transom height on a couple SIBs myself, for a couple years at least! The sandwich method looks like it will work okay, but then again, my outboard clamps would never open enough to handle the extra thickness. I would use 1/4" aluminum plate for the bread, and maybe HDPE boat board for the filling. Both of those are easily cut with standard woodworking tools, so no elaborate machine shop setup is necessary. What I finally found worked best for me was a 10" length of 3x3 aluminum angle mounted to the back of the transom, flush with the bottom of the transom. No need to adjust the transom height at all... That tiny little piece of aluminum made all the difference in the world!
you don't need anything that fancy on a SIB though respect for such a professional looking job. You can whack something together in an hour just to extend the transom, slip on and off and easy to experiment with only four stainless bolts and 5 pieces of pretty much any old wood that has the right thickness. One bit across the top as the extension with two holes in each end for the "legs". Then attach four bits of wood as legs to slip over the transom and just slip it on when you need it and no need to drill holes in the transom. I built that exact thing for my SIB and outboard yesterday in well under an hour just using scrap wood. I'll paint it with marine paint probably but even if it rots away I just make another.
Looks like a great solution - neat and tidy. I am kind of new to SIBs, but very happy I went that route. I am having a similar problem with a 430 SIB (I have at least two passengers each trip and a dog; total weight of everything, 700-800 lb.) and a Tohatsu MFS20eefs with 16.3" transom spec. On the trailer the cavitation plate sits 1.25" below the keel, on the water it seems more since the SIB raises at the front before plane as it should; changing manual trim does not appear to improve performance (trim hole 3 to 2 or 4). SIB/Tohatsu will start plane at 12-13 mph, below that the wake is enormous, on plane it is good and level, just unexpectedly slow (21 mph; according to phone app and RPMs are 5400 according to the meter I bought - which may or may not be a good measurement lol; Something I need to look into with the RPM meter although idle speed is reported as 960 rpm which is spot on.) and with the cavitation plate being well under water, no porpoising though, very smooth. Considering testing with shims above the transom to raise it 0.5-1.0" and if this improves speed I will try a more permanent solution. On another note, we went out this afternoon, and I had not realized how much the pressure changes according to temperature! There are 5+1 chambers in this 430 SIB, and as expected after launch some chambers were lower pressure due to water cooling and that was corrected (ambient T was in the late 80's). In fact the keel was more affected since it has the most water cooling effect. Later in the day, ambient T fell (70s) and so did the pressure in the tubes, so they were re-pressurized. Tube pressure affected speed and performance for sure. Ugh, TN weather, 95F one minute, 70F the next ...
Cheers mate. It doesn't look out of place which was the idea. Time will tell how long it stands up to the job, but will always tether to both eyelets as you just never know 😂
No, makes no difference really. I did strengthen it further with 3mm stainless steel plates either side for extra piece of mind. Always lock to the transom eyelets too of course nobody wants to lose an engine haha
My set up is exactly as you have described, the transom on my SIB is 15 inches and the shaft on my Suzuki 6 HP is 18 inches, therefore the cavitation plate sits 3 inches lower, in the water. Did your new transom riser make a huge difference in terms of performance?
Yep a good 4mph, hits around 19mph now, much cleaner tighter less V looking wake. Less spray, faster hole shot. I replaced the riser with 2 stainless steel sheets 5mm thick though but kept this just incase. It was too thick and barely any space to mount outboard and screw bolts
Hello, I can't resist, I should ask you a question. Can you plane at half throttle ? I have a 280 sib with 5hp outboard. And I'm almost planning with 2 people at full throttle but it's not enough. I'm sure it would be better but I'm asking myself how much it will increase my performances. If you answer me that you need more than half throttle to plane I'll take in consideration replacing my outboard for stronger one. But I would like to avoid this. Thanks in advance if you can let me know.
A 6hp wouldnt plane with 2 adults. You'd need 8hp+... A 5hp will probs max speed 11mph with 1 adult, will never plane with 2 adults. I have a 4hp yamaha that maxes 7-9mph but can't plane ever. You'll need more power. I can do 20mph now, half throttle and it's on plane as it has the power to get over the wave quickly.
Hi. It did, however I slightly changed it by using a 3mm stainless steel sheet on the outside and a 2mm sheet on the inside along with the marine ply. Much stronger and able to clamp bolts better. Before there was like 2mm spare to attach outboard clamp 👍
you don't need anything that fancy on a SIB though respect for such a professional looking job. You can whack something together in an hour just to extend the transom, slip on and off and easy to experiment with only four stainless bolts and 5 pieces of pretty much any old wood that has the right thickness. One bit across the top as the extension with two holes in each end for the "legs". Then attach four bits of wood as legs to slip over the transom and just slip it on when you need it and no need to drill holes in the transom. I built that exact thing for my SIB and outboard yesterday in well under an hour just using scrap wood. I'll paint it with marine paint probably but even if it rots away I just make another.
Why would you round the edges of an oak block getting sandwiched between sheets of plywood? The resulting grooves will draw in water and cause rot, especially since oak is prone to rot in the first place. Too many other things wrong with this design to mention.
@UguysRnuts I changed the design in the end, kept the oak block, preserved twice and painted several times over, using 1 sheet of marine ply with a 2mm stainless steel 304 sheet, and on the opposite side a 5mm stainless sheet, bolted together the same, and sealed all around. The idea is there though. Obviously it's better to use stronger materials if you can afford, cut, file or source them. Oak and mahogany are excellent hardwoods to use and English oak takes forever to rot lol
Been fiddling with transom height on a couple SIBs myself, for a couple years at least! The sandwich method looks like it will work okay, but then again, my outboard clamps would never open enough to handle the extra thickness. I would use 1/4" aluminum plate for the bread, and maybe HDPE boat board for the filling. Both of those are easily cut with standard woodworking tools, so no elaborate machine shop setup is necessary. What I finally found worked best for me was a 10" length of 3x3 aluminum angle mounted to the back of the transom, flush with the bottom of the transom. No need to adjust the transom height at all... That tiny little piece of aluminum made all the difference in the world!
you don't need anything that fancy on a SIB though respect for such a professional looking job. You can whack something together in an hour just to extend the transom, slip on and off and easy to experiment with only four stainless bolts and 5 pieces of pretty much any old wood that has the right thickness. One bit across the top as the extension with two holes in each end for the "legs". Then attach four bits of wood as legs to slip over the transom and just slip it on when you need it and no need to drill holes in the transom. I built that exact thing for my SIB and outboard yesterday in well under an hour just using scrap wood. I'll paint it with marine paint probably but even if it rots away I just make another.
True. But for a big rise of 6cm you do or it'll rip off eventually or screw up the transom a bit, especially 40kg on the back
Looks like a great solution - neat and tidy. I am kind of new to SIBs, but very happy I went that route. I am having a similar problem with a 430 SIB (I have at least two passengers each trip and a dog; total weight of everything, 700-800 lb.) and a Tohatsu MFS20eefs with 16.3" transom spec.
On the trailer the cavitation plate sits 1.25" below the keel, on the water it seems more since the SIB raises at the front before plane as it should; changing manual trim does not appear to improve performance (trim hole 3 to 2 or 4). SIB/Tohatsu will start plane at 12-13 mph, below that the wake is enormous, on plane it is good and level, just unexpectedly slow (21 mph; according to phone app and RPMs are 5400 according to the meter I bought - which may or may not be a good measurement lol; Something I need to look into with the RPM meter although idle speed is reported as 960 rpm which is spot on.) and with the cavitation plate being well under water, no porpoising though, very smooth. Considering testing with shims above the transom to raise it 0.5-1.0" and if this improves speed I will try a more permanent solution.
On another note, we went out this afternoon, and I had not realized how much the pressure changes according to temperature! There are 5+1 chambers in this 430 SIB, and as expected after launch some chambers were lower pressure due to water cooling and that was corrected (ambient T was in the late 80's). In fact the keel was more affected since it has the most water cooling effect. Later in the day, ambient T fell (70s) and so did the pressure in the tubes, so they were re-pressurized. Tube pressure affected speed and performance for sure. Ugh, TN weather, 95F one minute, 70F the next ...
2 adults at 21mph? In a 4.3m? That's good. 6000 be max rpm but most don't need to hit that unless smaller pitch props etc
I get 17mph on a 3m with a 5hp 4stroke mercury 2 man up
An Excellent video - Thanks/ Eamonn- Galway/ Ireland
Hi. Helpful video. Where can I get the plastic spacer sheets you used behind the pressure plate, please?
Bob
Very cool. Factory like work to be proud of.
Thank you ! Actually you made an engineer work ❤️😍
Well done 👏 looks great. 👍
Cheers mate. It doesn't look out of place which was the idea. Time will tell how long it stands up to the job, but will always tether to both eyelets as you just never know 😂
superb that's what I need to do for mine but will it effect the folding of the sib as that's the only way I can store it
No, makes no difference really. I did strengthen it further with 3mm stainless steel plates either side for extra piece of mind. Always lock to the transom eyelets too of course nobody wants to lose an engine haha
Looks good. I have a short shaft on a 15” transom and the motor is too long. It’s a Suzuki 6hp and actually measures 17” not 15” 🤔
This looks amazing! @ENG Dyna, what did you use for screw top covers (the white caps)?
Did it make any difference tho! Apart from splashing?
My set up is exactly as you have described, the transom on my SIB is 15 inches and the shaft on my Suzuki 6 HP is 18 inches, therefore the cavitation plate sits 3 inches lower, in the water. Did your new transom riser make a huge difference in terms of performance?
Yep a good 4mph, hits around 19mph now, much cleaner tighter less V looking wake. Less spray, faster hole shot. I replaced the riser with 2 stainless steel sheets 5mm thick though but kept this just incase. It was too thick and barely any space to mount outboard and screw bolts
@@ENGDyna That's brilliant.
Hello,
I can't resist, I should ask you a question. Can you plane at half throttle ?
I have a 280 sib with 5hp outboard. And I'm almost planning with 2 people at full throttle but it's not enough. I'm sure it would be better but I'm asking myself how much it will increase my performances.
If you answer me that you need more than half throttle to plane I'll take in consideration replacing my outboard for stronger one. But I would like to avoid this. Thanks in advance if you can let me know.
A 6hp wouldnt plane with 2 adults. You'd need 8hp+... A 5hp will probs max speed 11mph with 1 adult, will never plane with 2 adults. I have a 4hp yamaha that maxes 7-9mph but can't plane ever. You'll need more power. I can do 20mph now, half throttle and it's on plane as it has the power to get over the wave quickly.
@@ENGDyna thanks a lot for your answer, I appreciate it.
Did it work? i am just considering the same mod, as i bought a longshaft engine by mistake.
Hi. It did, however I slightly changed it by using a 3mm stainless steel sheet on the outside and a 2mm sheet on the inside along with the marine ply. Much stronger and able to clamp bolts better. Before there was like 2mm spare to attach outboard clamp 👍
@@ENGDyna Thanks for replying with the info.
you don't need anything that fancy on a SIB though respect for such a professional looking job. You can whack something together in an hour just to extend the transom, slip on and off and easy to experiment with only four stainless bolts and 5 pieces of pretty much any old wood that has the right thickness. One bit across the top as the extension with two holes in each end for the "legs". Then attach four bits of wood as legs to slip over the transom and just slip it on when you need it and no need to drill holes in the transom. I built that exact thing for my SIB and outboard yesterday in well under an hour just using scrap wood. I'll paint it with marine paint probably but even if it rots away I just make another.
Hi mate , did you notice much running difference after doing this?
Hey mate. Yeah definitely, have a look at some of my replies on here 👍
Why would you round the edges of an oak block getting sandwiched between sheets of plywood? The resulting grooves will draw in water and cause rot, especially since oak is prone to rot in the first place. Too many other things wrong with this design to mention.
@UguysRnuts I changed the design in the end, kept the oak block, preserved twice and painted several times over, using 1 sheet of marine ply with a 2mm stainless steel 304 sheet, and on the opposite side a 5mm stainless sheet, bolted together the same, and sealed all around. The idea is there though. Obviously it's better to use stronger materials if you can afford, cut, file or source them. Oak and mahogany are excellent hardwoods to use and English oak takes forever to rot lol
@@ENGDyna Whatever you say Skipper. LOL
@@UguysRnuts cheers Pedroooo