There has been several threads on a OB motor wedge. Some tilt the motor back to find the "sweet spot". This would seam to put undue strain on the tilt, right? There is also the problem of the bow raising. So my question is - What is the best angle of the motor? 90 degrees? 85? 95?(to bring the bow down, stern up)
How is this best achieved?
OB motor wedge?
I can't speak for the 26's, but the 
has a near vertical transom, and certainly can use some additional angle to bring the bow down as much as possible when motoring. We are having a new (to us) motor installed next week and are including a reversible wedge plate from Panther Marine to give us another 5 degrees of "tuck. I'm curious myself if it will make much of a difference.
Incidentally, the issue was discussed extensively on the Mac19 Yahoo group, and it seems the consensus was that the ideal is somewhere between 5 and 10 degrees extra -- though I'm sure the 26 is probably different.
has a near vertical transom, and certainly can use some additional angle to bring the bow down as much as possible when motoring. We are having a new (to us) motor installed next week and are including a reversible wedge plate from Panther Marine to give us another 5 degrees of "tuck. I'm curious myself if it will make much of a difference.Incidentally, the issue was discussed extensively on the Mac19 Yahoo group, and it seems the consensus was that the ideal is somewhere between 5 and 10 degrees extra -- though I'm sure the 26 is probably different.
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cbhinkel
- Deckhand
- Posts: 42
- Joined: Thu Jan 15, 2004 3:40 pm
- Location: Mac19 w/ Honda BF50; Escondido, CA
When I had my 26X with a Honda BF50, the measured transom wedge needed to make the cavitation plate parallel to the hull bottom was somewhere in the 10-15 degree range. The transom wedge that I eventually fabricated for that boat was about 20 degrees of induced tuck.
Motoring at the 10-15 degrees of trim produced a much more stable ride and reduced the porpoising and rocking that was there before. When the seas where over 3ft, I would trim the full 20 degrees which would push the bow into the oncoming swells. This reduced the famous "hull-smack" that 26Xs do when it gets rough and your are motoring quickly. It essentially allowed me to go about 2-3mph faster in higher seas without risking any additional shock loading onto the boat.
Motoring at the 10-15 degrees of trim produced a much more stable ride and reduced the porpoising and rocking that was there before. When the seas where over 3ft, I would trim the full 20 degrees which would push the bow into the oncoming swells. This reduced the famous "hull-smack" that 26Xs do when it gets rough and your are motoring quickly. It essentially allowed me to go about 2-3mph faster in higher seas without risking any additional shock loading onto the boat.
James, the "best" or optimal angle of the motor is 90 degrees to the direction of travel (i.e. the surface of the water), so that the the prop shaft is parallel with the direction of travel. At that angle, the highest amount of the motor's thrust is being used to push the boat forward. Because the prop is below the center of pressure the hull is riding on, some of the prop thrust goes toward lifting the bow.
The optimal angle of the motor frequently does not coincide with the optimal angle of the hull. Getting close to the latter isn't difficult with the trim adjustment. For any given throttle setting, trim up and down until you find the point of maximum motor rpm. The higher rpm tells you that the boat's drag in the water and the load on the motor is the lowest. If you trim down from this (aka trim "in" because the motor leg is coming "in" closer to the transom), this puts more of the hull bottom in the water, increases drag and the load on the motor, and causes the rpm to drop. If you trim up ("out") from this optimal point, it forces the boat's stern deeper in the water and increases the hull's angle of attack, also increasing drag and the load on the motor, and causes the rpm to drop. Under normal planing conditions, the boat's speed will follow the change in rpm.
The trim system is designed to carry the thrust of the motor... that's what it's there for, so you aren't hurting it by operating it as intended. OTOH, if you operate the motor trimmed all the way down on the pin designed to stop it from going further down, you're transmitting a lot more vibration into the hull. Furthermore, operating the boat with the motor trimmed for other than optimal hull angle increases the load and wear on the motor, not to mention increases fuel consumption.
There are conditions where operating with down trim is called for. A prime example is a lightweight skiff with one person aboard steering a tiller-steered outboard with the fuel tank, and worse yet, a battery, aft. Such a boat will tend to ride very bow high and porpoise, even if the motor is trimmed up only slightly up from full down.
While that's an extreme example, there are runabouts and even center consoles that have a stern-heavy problem, especially those with large fuel tanks in the bilge right in front of the transom. A common band-aid for this balance problem is the motor hydrofoil, which provides some stern lift and allows the motor to be trimmed up, with the prop shaft closer to parallel with the line of travel. However, with lift comes drag so that gain in forward thrust from a more upright outboard mostly just offsets the increased drag from the foil.
Obviously, when a powerboat is in transition from hull speed to planing, before it's rolled over and the bow has dropped, full down trim helps lower the steep angle of attack and accelerates the boat more forward rather than upward climbing the bow wave. Anything less than full down trim wil usually cause a decrease in rpm as a result of the drag.
And as mentioned, in heavy seas it's often desirable to trim down somewhat to keep a hull's deeper forward V cutting into waves, rather than have them impact further aft where the V is flatter. The problem with going too far in this direction is that it can cause bow steering.
You can't compare the 19 to the 26 powersailors. The former is a powerboat hull with little compromise for sailing. Pull up the drawings and pictures from the brochures off the MacGregor Sailing site. The 19 has a straight bottom and hard, powerboat chines. The X introduced "rocker" into the hull bottom to have less of the flat, drag-inducing transom in the water for better sailing speed. Notice how rounded (convex) it is in the side view compared to the 19. Softer chines were also introduced to try to minimize the change in hull shape during heeling. The cost of both changes is relatively less lift at the stern, and a higher bow at the optimal hull angle. The M carried this transition away from the powerboat hull a little further, with even softer chines and a deeper keel for a more rounded hull shape.
The 19 also carries its forward deeper-V further back than the 26s and takes less down trim to cut through heavier seas. The X bottom begins flattening almost all the way up at the bow, so down trim in waves is less effective. In fact, down trimming a boat with rocker like the X lifts the stern, putting less of it in the water. With the soft chines (for a powerboat), this compounds the longitudinal stability problem.
You can't expect a hull with rocker to ride as bow down as one with a flatter bottom. If you can achieve optimal hull angle, i.e. peak rpm, by trimming the motor up from full down, you probably don't need a wedge. If you can't, maybe you do need one, but I'd try redistributing the load forward first.
The optimal angle of the motor frequently does not coincide with the optimal angle of the hull. Getting close to the latter isn't difficult with the trim adjustment. For any given throttle setting, trim up and down until you find the point of maximum motor rpm. The higher rpm tells you that the boat's drag in the water and the load on the motor is the lowest. If you trim down from this (aka trim "in" because the motor leg is coming "in" closer to the transom), this puts more of the hull bottom in the water, increases drag and the load on the motor, and causes the rpm to drop. If you trim up ("out") from this optimal point, it forces the boat's stern deeper in the water and increases the hull's angle of attack, also increasing drag and the load on the motor, and causes the rpm to drop. Under normal planing conditions, the boat's speed will follow the change in rpm.
The trim system is designed to carry the thrust of the motor... that's what it's there for, so you aren't hurting it by operating it as intended. OTOH, if you operate the motor trimmed all the way down on the pin designed to stop it from going further down, you're transmitting a lot more vibration into the hull. Furthermore, operating the boat with the motor trimmed for other than optimal hull angle increases the load and wear on the motor, not to mention increases fuel consumption.
There are conditions where operating with down trim is called for. A prime example is a lightweight skiff with one person aboard steering a tiller-steered outboard with the fuel tank, and worse yet, a battery, aft. Such a boat will tend to ride very bow high and porpoise, even if the motor is trimmed up only slightly up from full down.
While that's an extreme example, there are runabouts and even center consoles that have a stern-heavy problem, especially those with large fuel tanks in the bilge right in front of the transom. A common band-aid for this balance problem is the motor hydrofoil, which provides some stern lift and allows the motor to be trimmed up, with the prop shaft closer to parallel with the line of travel. However, with lift comes drag so that gain in forward thrust from a more upright outboard mostly just offsets the increased drag from the foil.
Obviously, when a powerboat is in transition from hull speed to planing, before it's rolled over and the bow has dropped, full down trim helps lower the steep angle of attack and accelerates the boat more forward rather than upward climbing the bow wave. Anything less than full down trim wil usually cause a decrease in rpm as a result of the drag.
And as mentioned, in heavy seas it's often desirable to trim down somewhat to keep a hull's deeper forward V cutting into waves, rather than have them impact further aft where the V is flatter. The problem with going too far in this direction is that it can cause bow steering.
You can't compare the 19 to the 26 powersailors. The former is a powerboat hull with little compromise for sailing. Pull up the drawings and pictures from the brochures off the MacGregor Sailing site. The 19 has a straight bottom and hard, powerboat chines. The X introduced "rocker" into the hull bottom to have less of the flat, drag-inducing transom in the water for better sailing speed. Notice how rounded (convex) it is in the side view compared to the 19. Softer chines were also introduced to try to minimize the change in hull shape during heeling. The cost of both changes is relatively less lift at the stern, and a higher bow at the optimal hull angle. The M carried this transition away from the powerboat hull a little further, with even softer chines and a deeper keel for a more rounded hull shape.
The 19 also carries its forward deeper-V further back than the 26s and takes less down trim to cut through heavier seas. The X bottom begins flattening almost all the way up at the bow, so down trim in waves is less effective. In fact, down trimming a boat with rocker like the X lifts the stern, putting less of it in the water. With the soft chines (for a powerboat), this compounds the longitudinal stability problem.
You can't expect a hull with rocker to ride as bow down as one with a flatter bottom. If you can achieve optimal hull angle, i.e. peak rpm, by trimming the motor up from full down, you probably don't need a wedge. If you can't, maybe you do need one, but I'd try redistributing the load forward first.
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Mark Prouty
- Admiral
- Posts: 1723
- Joined: Mon Jan 19, 2004 8:52 am
- Location: Madison, WI Former MacGregor 26X Owner
Danger Will Robinson! Danger!
Danger Will Robinson! Danger!!
I installed a hydrofoil on my larger motor. It works well despite the danger warnings. But don't say I didn't warn ya.
Trims the bow on command. I don't feel it would work on a 50hp. For max speed and horse power there is a definate feel to the trim. I get her going and tilt up the motor until I hit the spot.
I installed a hydrofoil on my larger motor. It works well despite the danger warnings. But don't say I didn't warn ya.
Trims the bow on command. I don't feel it would work on a 50hp. For max speed and horse power there is a definate feel to the trim. I get her going and tilt up the motor until I hit the spot.
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cbhinkel
- Deckhand
- Posts: 42
- Joined: Thu Jan 15, 2004 3:40 pm
- Location: Mac19 w/ Honda BF50; Escondido, CA
Moe,
Several things, what the heck is bow steer ( I don't know about your bow, but my bow will only point me straight ahead)? Two, I've owned an X boat for four years and did some pretty extensive mods on it. The transom wedge I "actually" added to it do helped alot in heavy seas despite your pure speculation that it wouldn't help at all. Three, MacGregor powersailors will never be great sailboats ever because of their compromise design. The Mac19 is definitely the worst but it doesn't get too much better with the 26X even though it has all of the extra "doo-dads" you mention iin its hull design and the jury is out if the M is any better. Roger Macgregor fooled me once when I bought my 26X, but with my Mac19, at least I can approach the 24mph top speed more easily than the 26' powersailors!
For pure speed, having the outboard's power 90 degrees to the direction travel is correct, like you stated. However, I disagree that it's the "best". In a 26X, for a more stable ride that actually won't significantly reduce top speed, alittle extra tuck does have a benefit. The 26X is one of the most tender boats I've ever been on and has made many of my invited guest seasick once I go on open waters. One more time, I actually did the tests with the additional engine trim (looking at speed and engine rpm etc.) and know the results. You are only guessing with what you just said! :>)
Now with my Mac19 and the V-hull and hard chines, the added trim is wonderful. No more hull smacking at all and it's a much drier ride to boot in comparison to my old 26X when the chop picks up. Once I get the right head sail, I'll be right up there with the 26' powersailors. We just had a post from a Mac19 individual how can get a consistent 8mph (by GPS) using a Hobie super jib by itself against a 3mph current. Seems a bit optimistic, but I pretty sure I can come up with a good solution along these lines.
Experience is key, blah-blah-blah is just blah-blah-blah!
-Chris
Several things, what the heck is bow steer ( I don't know about your bow, but my bow will only point me straight ahead)? Two, I've owned an X boat for four years and did some pretty extensive mods on it. The transom wedge I "actually" added to it do helped alot in heavy seas despite your pure speculation that it wouldn't help at all. Three, MacGregor powersailors will never be great sailboats ever because of their compromise design. The Mac19 is definitely the worst but it doesn't get too much better with the 26X even though it has all of the extra "doo-dads" you mention iin its hull design and the jury is out if the M is any better. Roger Macgregor fooled me once when I bought my 26X, but with my Mac19, at least I can approach the 24mph top speed more easily than the 26' powersailors!
For pure speed, having the outboard's power 90 degrees to the direction travel is correct, like you stated. However, I disagree that it's the "best". In a 26X, for a more stable ride that actually won't significantly reduce top speed, alittle extra tuck does have a benefit. The 26X is one of the most tender boats I've ever been on and has made many of my invited guest seasick once I go on open waters. One more time, I actually did the tests with the additional engine trim (looking at speed and engine rpm etc.) and know the results. You are only guessing with what you just said! :>)
Now with my Mac19 and the V-hull and hard chines, the added trim is wonderful. No more hull smacking at all and it's a much drier ride to boot in comparison to my old 26X when the chop picks up. Once I get the right head sail, I'll be right up there with the 26' powersailors. We just had a post from a Mac19 individual how can get a consistent 8mph (by GPS) using a Hobie super jib by itself against a 3mph current. Seems a bit optimistic, but I pretty sure I can come up with a good solution along these lines.
Experience is key, blah-blah-blah is just blah-blah-blah!
-Chris
Mercury Outboard Owners Manual wrote:Trimming In or Down can... In excess, lower the bow of some boats to a point at which they begin plow with their bow in the water while on plane. This can result in an unexpected turn in either direction (called "bow-steering" or "oversteering")...
WARNING: Avoid possible injury or death. Adjust outboard to an intermediate trim position as soon as boat is on plane to avoid possible ejection due to boat spin-out...
Where did I speculate it wouldn't help at all, Chris? Saying that it's less effective on the 26X than the 19 isn't saying it doesn't help at all.chinkel wrote:...it do helped alot in heavy seas despite your pure speculation that it wouldn't help at all.
The only speculation in that post is where I said "probably."chinkel wrote:You are only guessing with what you just said! :>)
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cbhinkel
- Deckhand
- Posts: 42
- Joined: Thu Jan 15, 2004 3:40 pm
- Location: Mac19 w/ Honda BF50; Escondido, CA
Okay, now that I know what "bow steering" is, the 26X will never have that occur because the boat is not capable of going onto a consistent plane in heavy seas. (heavy seas defined as 5ft+, small craft advisory ocean swells, not just lake chop) 6.0mph is probably the max and I was able to up to 8mph with my 26X and full 15-20 degrees trim, not even close to planing speed. I don't want people here to get concerned they are going to have bow steering problems if they decide to modify their boats to have high trim capabilities. I personally believe this mod makes the 26X safer with a more stable ride.
Moe wrote:
Moe wrote:
Lastly, the second half of your long post is mostly against having a high level of trim and you go into several paragraphs discussing the theory of why you shouldn't do that with hull designs and the like, all being pure speculation as you never have personally tested anything that was stated.
In conclusion to what I had on my old 26X, I first started with a transom wedge of 25 degrees but after testing, realized that was a bit too much and modified to have a total trim capacity somewhere in the 15-20 degree range. I wanted my boat to have the best planing characteristics and highest top speed, highest outboard rpm with the Honda trim meter pointing at the halfway point, which is what I ended up with. Although, this trim setting was only utilized on very smooth waters. I generally had the trim set a 3/4 bow down as that still had good speed, but made the boat more stable with less roll. And like I stated before, I would trim all of the way down in really rough conditions to allow a greater hull speed and even more stability.
Moe wrote:
Right here:Where did I speculate it wouldn't help at all, Chris? Saying that it's less effective on the 26X than the 19 isn't saying it doesn't help at all.
Moe wrote:
I wasn't even talking about my Mac19 with my first post in this thread. It was mostly about my personal experience with my 26X.You can't compare the 19 to the 26 powersailors.
Lastly, the second half of your long post is mostly against having a high level of trim and you go into several paragraphs discussing the theory of why you shouldn't do that with hull designs and the like, all being pure speculation as you never have personally tested anything that was stated.
In conclusion to what I had on my old 26X, I first started with a transom wedge of 25 degrees but after testing, realized that was a bit too much and modified to have a total trim capacity somewhere in the 15-20 degree range. I wanted my boat to have the best planing characteristics and highest top speed, highest outboard rpm with the Honda trim meter pointing at the halfway point, which is what I ended up with. Although, this trim setting was only utilized on very smooth waters. I generally had the trim set a 3/4 bow down as that still had good speed, but made the boat more stable with less roll. And like I stated before, I would trim all of the way down in really rough conditions to allow a greater hull speed and even more stability.