I got my motor mount rebuilt with new bushings and new bolts do you mount it so the cavitation plate lines up with the bottom of boat as on a power boat or do I need to go lower. This is a new to my mount so I can't use the old mounting holes .
Motor mount?
- Thread starter slowdog
- Start date
I'd think you'd go lower as you're not trying to get up on a plane or break any speed records as you would on a power boat.
Slowdog, here's my take on it.
Powerboats want the anti-ventilation plate at the bottom of the transom, because they want the lower unit in the water, but only as much in the water as needed. Less friction = better planing, more speed. Race boats have jack plates to allow the motor to be lifted while underway to have the least amount of motor in the water for speed.
With sailboats, we don't need to worry about that. Our primary concern for non-planing craft that don't ride with a stern down/bow up attitude, is keeping the prop in the water as much of the time as possible. When you get out in rougher water, the design of a sailboat is such that the boat will tend to hobby-horse to some extent, pitching around a point roughly amidships, which provides a pretty long lever arm to lift the stern out of the water, and also lifting the prop out of the water. This is one of the main drawbacks to having outboard power for a sailboat (as well as hanging weight of the stern, and usually to one side of the boat.) This is why the "sail pro" versions of many smaller motors have a 25" extra long shaft, instead of the usual 20" or 22" long shaft. (Short shafts are usually about 15".) An extra long shaft gains 5" of depth, which could make the difference between powering through waves, or the boat pitching over a wave and ventilating the prop.
All that's really going on down the shaft is water pump intakes in the lower unit. Most motors nowadays exhaust through the prop to cut down on noise and improve efficiency a little bit. Some motors may still have an exhaust port about halfway up the shaft - but probably not. Keeping this port out of the water would be a good thing. But other than that, having a mount that can keep the anti-ventilation plate several inches below the bottom of the transom is pretty much a good thing on a sailboat.
One thing that can also be a consideration (on any boat, including power) is that the powerhead of the motor is not so low that it can be pooped by waves from astern. Luckily, with the shapes of many sailboats, this is less likely to happen, and the boat does tend to pitch whereas powerboats have a flat transom waves can slap against.
But I think for the majority of outboard powered sailboats, flooding the powerhead with a running sea isn't a terribly major concern, as much as having the prop low enough to prevent lift out.
Brian
Powerboats want the anti-ventilation plate at the bottom of the transom, because they want the lower unit in the water, but only as much in the water as needed. Less friction = better planing, more speed. Race boats have jack plates to allow the motor to be lifted while underway to have the least amount of motor in the water for speed.
With sailboats, we don't need to worry about that. Our primary concern for non-planing craft that don't ride with a stern down/bow up attitude, is keeping the prop in the water as much of the time as possible. When you get out in rougher water, the design of a sailboat is such that the boat will tend to hobby-horse to some extent, pitching around a point roughly amidships, which provides a pretty long lever arm to lift the stern out of the water, and also lifting the prop out of the water. This is one of the main drawbacks to having outboard power for a sailboat (as well as hanging weight of the stern, and usually to one side of the boat.) This is why the "sail pro" versions of many smaller motors have a 25" extra long shaft, instead of the usual 20" or 22" long shaft. (Short shafts are usually about 15".) An extra long shaft gains 5" of depth, which could make the difference between powering through waves, or the boat pitching over a wave and ventilating the prop.
All that's really going on down the shaft is water pump intakes in the lower unit. Most motors nowadays exhaust through the prop to cut down on noise and improve efficiency a little bit. Some motors may still have an exhaust port about halfway up the shaft - but probably not. Keeping this port out of the water would be a good thing. But other than that, having a mount that can keep the anti-ventilation plate several inches below the bottom of the transom is pretty much a good thing on a sailboat.
One thing that can also be a consideration (on any boat, including power) is that the powerhead of the motor is not so low that it can be pooped by waves from astern. Luckily, with the shapes of many sailboats, this is less likely to happen, and the boat does tend to pitch whereas powerboats have a flat transom waves can slap against.
But I think for the majority of outboard powered sailboats, flooding the powerhead with a running sea isn't a terribly major concern, as much as having the prop low enough to prevent lift out.
Brian
Slowdog,
1. I like your handle man.
2. the important part as the guys have advised, is ALIGNMENT ANGLE FROM THE ENGINE COUPLER FLANGE TO THE PROP.
This should be priority #1. There's non-other.
You need to make sure of the alignment or talk with someone who knows how to achieve this.
CR
1. I like your handle man.
2. the important part as the guys have advised, is ALIGNMENT ANGLE FROM THE ENGINE COUPLER FLANGE TO THE PROP.
This should be priority #1. There's non-other.
You need to make sure of the alignment or talk with someone who knows how to achieve this.
CR