Motor trim tab

[Dimitri-2000X-Tampa]

The way you find this is to run WOT, trimming up from full down, a little at a time, pausing to let the boat stabilize. As you trim up, RPM and speed will rise as the drag decreases, until it doesn't rise any more, and may eventually start to fall. Note the motor's attitude at the point that RPM and speed just stop rising.

If it isn't vertical, and the propellor shaft parallel with the water, you're sacrificing forward thrust to compensate for an unbalanced boat.

This is probably good wisdom for conventional speedboats, but I have a feeling that our macs are designed to be stern heavy. Something about a planing sailboat I'm sure. Ever notice when planing, how the bow is lifted up quite a bit more than a normal speedboat?

I've tried trimming the motor up in many configurations...including with 3 or 4 kids standing in the V-berth, my wife on the front port seat and only me in the cockpit. This should put a pretty fair amount of weight in the bow. I also have a 26 gal water tank under the foreward dinette seat to bring weight forward. It always goes fastest with the motor in the all the way down position. Anybody get different results than this? I've since given up on trim adjustments and always run with it fully down....except for the occasional time that I was running in shallow water with the engine trimmed up, and then forgot to put it back down later.

[Moe]

There are some boats that are just too stern heavy to balance properly. This includes the smaller Boston Whaler Dauntless models, with huge sub-deck gas tanks back in front of the transom. These boats usually benefit from trim tabs, althouth I don't see any place to put them on a MacGregor. There are a couple of manufacturers of bolt-on (no drilling) motor hydrofoils, and these seem to help allow these boats to be trimmed out to at least vertical.

I actually balance my little Whaler bow-heavy intentionally at times. It's not a Dauntless, having only two 6.6 gallon tanks under the helm seat.

With the roughly 50 lb 50 quart cooler tied down behind the helm seat, the motor is almost vertical at the WOT peak RPM and speed. It's just past vertical in a very slight bow lift, probably due to the two anchors and chain I carry in the bow locker.

But when we're going out in rough water, rather than have the motor trimmed in (down) to hold the bow down into the waves, I move the cooler up to tie-downs just behind the bow locker. This allows the motor to be vertical at the less than WOT speed we run in big chop. This relieves the motor of the tremendous load of running trimmed down constantly.

However, if I use this cooler forward setup on calm water, the motor has to be trimmed WAY out past vertical to get peak RPM and speed, and it costs me 200 rpm and almost 2 mph at peak.

I also use different props for different conditions, and carry the other as a spare. Takes less than 5 minutes to change them (in the garage) .

As I've said before, with my lard ass on the helm seat, 24 gallons of gas, and a four-stroke motor, I'm betting we have the same stern-heavy problem with our X.

--
Moe

[Mark Prouty]

The way you find this is to run WOT, trimming up from full down, a little at a time, pausing to let the boat stabilize. As you trim up, RPM and speed will rise as the drag decreases, until it doesn't rise any more, and may eventually start to fall. Note the motor's attitude at the point that RPM and speed just stop rising.

If it isn't vertical, and the propellor shaft parallel with the water, you're sacrificing forward thrust to compensate for an unbalanced boat.

This is probably good wisdom for conventional speedboats, but I have a feeling that our macs are designed to be stern heavy. Something about a planing sailboat I'm sure. Ever notice when planing, how the bow is lifted up quite a bit more than a normal speedboat?

I've tried trimming the motor up in many configurations...including with 3 or 4 kids standing in the V-berth, my wife on the front port seat and only me in the cockpit. This should put a pretty fair amount of weight in the bow. I also have a 26 gal water tank under the foreward dinette seat to bring weight forward. It always goes fastest with the motor in the all the way down position. Anybody get different results than this? I've since given up on trim adjustments and always run with it fully down....except for the occasional time that I was running in shallow water with the engine trimmed up, and then forgot to put it back down later.

Keep the crew weight aft, low in the boat, and centered from side to side. Keep the crew in the cockpit, sitting down. The rear of the hull is relatively flat, and the nose area has a deep V to allow the boat to slide through waves with less slamming. If there is a lot of crew weight forward, the flat part of the hull bottom, which normally provides the stability, is raised higher out of the water, and is less effective in providing sideways stability. With the crew weight forward, the nose is depressed. The deep V nose shape does not contribute much to stability. When excess weight is at the front of the boat, the less stable nose area is carrying more of the weight of the boat and crew, the boat becomes far more easily capsized. Keep weight off of the forward V berth when under way, and avoid storing heavy items under the V berth. Crew members on the foredeck or cabin top are far more likely to get bounced out of the boat than those in the cockpit or inside the cabin. Anyone on the cabin top will have a natural tendency to grab the mast or mast support wires if the boat tips. That puts a heavy load high on the mast and tends to lever the boat over. Keep the weight low. Obviously, it is best to have the crew positioned so the boat sits or rides level rather than leaning to one side or the other.

IMHO, this boat is made to ride bow high. I keep the motor trimmed down for fastest speed - maybe a touch up.

[Tom Spohn]

One trick we learned with our X was to lower the motor all the way till it hits the stop, then tap the "up" key just enough to get it off the stop--maybe 1/4 inch. This will reduce vibration and noise with the Tohatsu 50.

[Moe]

IMHO, this boat is made to ride bow high. I keep the motor trimmed down for fastest speed - maybe a touch up.

Mark, if the boat is _made_ to ride bow high, why are you lowering the bow with the down-trimmed motor

I'm going to guess that on most Mac setups, one of the reasons for the bow-high tendency is that the outboard is mounted all the way down on the transom, giving the line of thrust more leverage to lift the bow, rather than being mounted up with the anti-ventilation plate even with the transom bottom.

Tom, MOST outboards will transmit a lot less vibration to any hull, if trimmed up off the down trim stop. That vibration is a better indication of full down (for those of us without a gauge) than the change in sound of the trim motor, which can be hard to hear at full throttle.
--
Moe

[Mark Prouty]

IMHO, this boat is made to ride bow high. I keep the motor trimmed down for fastest speed - maybe a touch up.

Mark, if the boat is _made_ to ride bow high, why are you lowering the bow with the down-trimmed motor

Moe

You got me on that one Moe. The bow does ride low with it trimmed all the way down. So I do tweek it up a bit to get the bow to ride higher Also, I have that hydrofoil on my engine so my I can't really compare trim positions. I like the hydrofoil because it lets me get the bow down. At slower speeds for visibility, this is beneficial. It also allows me to get on plane faster. You pointed out in a previous thread that this hydrofoil shouldn't be too low in the water. I took a look and it does ride a couple of inches below the transom. I'm going to remove this hydrofoil and am getting a 7 degree shim installed. This shim should do what the hydrofoil does.

[Moe]

I'm going to remove this hydrofoil and am getting a 7 degree shim installed. This shim should do what the hydrofoil does.

If you mean lower the bow, yes, it will... but at the expense of forward thrust. I think I'd keep the hydrofoil and raise the motor so the hydrofoil is operating where it should be.

--
Moe

[Moe]

If we're talking about what the X was _designed_ to do, I'm betting that it was designed to have proper attitude for maximum speed, with the motor trimmed vertical, with the original, probably sub-200 lb, 50HP Tohatsu two-stroke (which I wouldn't be surprised to find was spec'd closer to 165 lbs than 200), and two 6 gallon, maybe even two 7.5 gallon so-called 9GAS, tanks of fuel.

With the four-strokes out there today, many of us are putting much more weight out behind the transom, and carrying twice that much in gas just ahead of it.

--
Moe

[Moe]

Boston Whaler corporate recommends the use of the Grand Isle (or is it Island, I forget) Marine Turbo-Lift for boats that require a motor foil. IMHO, they're butt-ugly on a black motor, compared to something like the Doel-Fin, which being black, just sorta disappears, but they don't look too bad on a silver one.

Picture 1, Picture 2, Picture 3, Picture 4, Picture 5, Picture 6

Owners report they like them better than the Doel-Fin or Sting-Ray for several reasons. First, there's no drilling of the AV plate. They clamp on. Second, they extend further back, giving more bow-down lever arm when the bow starts to rise.

One downside is that they aren't available for all motors. Given the lower unit of the BigFoot is the same as the 75-115HP Mercs, they probably have one for it. And they don't have a website, just a phone number (321) 452-8126

--
Moe

[Dimitri-2000X-Tampa]

As I've mentioned in other threads, I'm pretty sure I gained about 0.5 mph of speed when I took the fins off of my motor. I used them for about the first year I owned the boat, and now have had them off for about 6 months. I don't notice that it takes any extra effort to get the boat on a plane without the fins. I believe the owners manual also recommends against these fins as an uneccessary gadget. I just filled in the holes on the cavitation plate with silicon sealer..and it is still there. Figured that might reduce the tiny bit of extra turbulence from the holes.

My boat also had 150# of dead weight (two mondo dumbbells) at the very tip of the bow under the vberth in the flotation. I took those out too and the boat got faster and much more laterally stable when not moving. The P.O. said the dealer was putting these on all his boats and swore up and down it made the boat handle better. It made the bow so low, I almost broke the front bunk off my trailer the first time I retrieved the boat...

The boat came with a 14X11 prop which I swapped for a 14X10. That increased my WOT RPM by 5-600...which is more than it was "supposed" to.

See, people have a tendency to fix what's not broke...I used to do it a lot more myself, but am getting away from it But as I systematically remove all this nonsense that the previous owner (or dealer) put on, I find myself going faster and faster. As I mentioned recently, I hit 19.7 last weekend for the first time..and I have a rough bottom job. When I first bought the boat, I don't think it could even hit 17 with just me on it!

[Jack O'Brien]

May I suggest that Dimitri's boat may not be stern heavy - it just can't quite get up on a true plane. It is stern low because it is still "plowing". Granted, it may plow less and plane more with more of the weight forward, but the basic problem is 50 HP isn't enough to plane an X.

[Moe]

[waternwaves]

I'll try not ot irritate the proponents nor the oponents of whether or not a mac planes with 50 hp, however... like many of us, I have afew boats also...

and to plane, the boat has to climb over its bow wave., that is what is holding the bow up....

and for those of you that do not think this is critical..... let me tell a story about another boat, designed to plane....

My 21 ft. Marlin has a little 5.7 liter, 270 hp, cruise weight with 4 adults around 4800 lbs, with an OMC king cobra outdrive, does a little over 45 mph....

improper loading, and I cannot get that boat on plane and it will run with the bow 8 ft in the air at 13 mph.......It literally has to climb out of huge hole with too much weight astern, and even that engine cannot push it over the top.

redistributing the weight allows me to take it up to 45 mph.... go figure...lol.

now for the mac, we have less than 1/5 that horsepower, similiar weight, I cannot stress how important weight distribution is on the mac. And watching both wakes (bow and stern) gives us a reference as to the amount of planing a given configuration can obtain, when properly trimmed. watch this for a while and you will even be able to reference and eventually estimate your loaded weight. Most of the macs I have watched (mine included) do not come down off the climb, at a normal cruise weight until 16 -17 mph. until then the nose is just too high, and both wakes are still being produced, not to mention teerrible fuel economy. Now, I also have noticed, when I have stripped it of much of the incidental weight, it is much flatter in cruise profile and gets to 20 mph quickly. oh.. and at the lighter weight the bow trims down at about 14-15.

Just an insight on how critical those 600-800 lbs can be. lbs can be...

[Dimitri-2000X-Tampa]

May I suggest that Dimitri's boat may not be stern heavy - it just can't quite get up on a true plane. It is stern low because it is still "plowing". Granted, it may plow less and plane more with more of the weight forward, but the basic problem is 50 HP isn't enough to plane an X.

Now what was it that Richard Dawson used to always say on that game show Family Feud.....

[Mark Prouty]