Midsection length and transom height

Peter Devil Ears · #1 (**permalink**) 12-30-2011, 07:50 AM

Hi, anyone know about the different lenghts of outboard midsections? I have a DT115 and the transom was modified before I purchased the boat. The anti air plate is level with the bottom of the boat as it should be, but the hole under the power head is submerged so that only the power head sticks out of the water, and so water gets in this hole, then the boat will not idle. Do I have a problem with the motor's tuning, or should this hole be out of the water? Perhaps the midsection is too short for this boat, I believe different length motors are available? Please help, it will be greatly appreciated.

boats.net · #2 (**permalink**) 12-30-2011, 08:22 AM

The midsection itself are the same lengths. The extra lengths come from a spacer between the midsection and the lower unit. There should be a good portion of your midsection out of the water. Sounds like you may have some rigging errors.

keakar · #3 (**permalink**) 12-30-2011, 12:03 PM

sounds like your bottom plugs are under water and not firing correctly because of it, this can also crack the porcelin of the plug if they get wet when they are really hot.

i believe you can add the extension spacer boats.net mentioned and have them replace the shaft with a longer one which should solve all your issues but check with your dealer if it will work.

if not you can see if you can work out a motor swap deal with a used motor dealer

noelm007 · #4 (**permalink**) 01-03-2012, 04:48 PM

If the cav plate is level with the bottom of the boat, then your motor is the correct length, so there is now a couple of possibilities, the motor is too heavy for the boat and it is sitting stern heavy, the boat is full of water and once again, sitting too stern heavy, is it possible for you to post a couple of pictures of your setup, from the side and from the rear? Oh and addding a spacer is NOT recomended unless the transom is designed for the longer shaft.

keakar · #5 (**permalink**) 01-03-2012, 07:15 PM

Quote:

Originally Posted by noelm007

If the cav plate is level with the bottom of the boat, then your motor is the correct length, so there is now a couple of possibilities, the motor is too heavy for the boat and it is sitting stern heavy, the boat is full of water and once again, sitting too stern heavy, is it possible for you to post a couple of pictures of your setup, from the side and from the rear? Oh and addding a spacer is NOT recomended unless the transom is designed for the longer shaft.

this is completely wrong to assume, what you should have said is: If the cav plate is level with the bottom of the boat, then your lower unit is at the correct mounting position so the motor was mounted properly on the boat but this has nothing to do with wether the height of the motor out of the water is correct based on floatation height.

i have sen many boats with odd floating habit so the motor sits too low to the water when not on a plane so only going by the tape measure it tells you a short shaft motor fits your boat but in fact you need a long shaft motor to keep the bottom of the power head sitting out of the water when at idle.

my old evenrude 90 was famous for that, if you walked to the transome the bottom two plugs went under water with the waves so i had to tilt the motor up anytime i needed to check something on the transome or crack those two plugs. it was SOP to carry a spare set of plugs in case i forgot.

noelm007 · #6 (**permalink**) 01-03-2012, 09:13 PM

nope, wrong, the extra 5" of shaft length does not make the motor an extra 5" out of the water if the motor cannot be mounted 5" higher because it has (say) a 20" transom, if you put a 25" motor on a 20" transom, you MAY be able to lift the motor another couple of holes (maybe) however, the prop will be deeper in the water, making a rooster tail when under way, the right motor is the right motor, no matter how you look at it, by your thinking, every boat should have a 30" leg fitted to it.

keakar · #7 (**permalink**) 01-04-2012, 03:10 PM

once again, apples to apples, if the motor is sitting in the water then its too low no matter what. if it fits the transom properly but the boat is too transom heavy then it will have isues from sitting too low in the water. adding 30 galons of gas, 2 batteries, and rear storage can lower the motor a good 4-5 inches in floatation height.

you wish to argue boat measurements when i am talking about floatation issues. have you ever heard of a jack plate? they arent only for bass boats and racing you know they also compensate for boats that have floatation issues wether its from loading, too heavy a motor on too light a boat, or just a bad design.

just as the cav plate should be even with the bottom of the hull if the motor is mounted correctly, the bottom of the power head should also never touch the water at idle if the motor sits out of the water correctly. there are two considerations and you cant only look at one of them because it is equally important that it fits the transom height as well as that it floats correctly.

noelm007 · #8 (**permalink**) 01-04-2012, 04:40 PM

OK, I give up, sure there is ways to fit a longer motor to a short transom, but the boat is too stern heavy, we need to know why, seems pretty simple to me, the motor is too big for the boat, or the boat is full of water.

Peter Devil Ears · #9 (**permalink**) 01-08-2012, 02:52 AM

Thanks for all the assistance, I really think from what I am hearing that the motor is too short, since the transom was modified by some jack a$$ that owned the boat before me. There is a good two inches of the transom plate cut off the top, obviously to make the cav plate sit right, which is the case. The manufacturing plate says that the max engine power for the boat is 150HP and this is a 115 so I assume the motor is not too big for the boat. I was thinking that I need to reverse this modification with some strong wood and some bolts and maybe support metal plates, then swap the motor or boat so that the match is correct. Any other options? Thanks for all the help. As for the boat being stern heavy, maybe, but there is that issue of the motor being smaller than the man plate indicates. Will take photos but I don't wanna go back to the water until sorted since it does not idle or run at low revs, the exhaust gets water in it due to this issue.

keakar · #10 (**permalink**) 01-08-2012, 04:02 AM

some boats are stern heavy by design or ultralight like an aluminum flat boat which if fitted with a 4 stroke will always sit too low.

as you described it, it sounds like you needed a long shaft and some idiot thought it was a good idea to just cut the transom without thinking about how low the boat sits in the water. he also likely got the cheapest deal, hence the wrong fitting short shaft undersized motor.

i would pay carefull attention to how well the transom was sealed and repaired since it sounds like some jackleg did it.

often the way new boats are rated, the max hp they list is in reality just the minimum size you should use. the reason is they rate them as is so there is no weight in the boat. add fishermen, ice chests, maybe a trawl and boards and it would take every bit of that 150 to push it and if i put a motor on a boat rated for 150 max hp i would use a 175 hp motor on it.

there is such a thing as too much motor on a boat but IMO go one size over the rated max gives you the best fit if you really use your boat, if your just boat riding and sking then the recommended max would serve you well enough.