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Old 11-14-2006, 08:41 PM   #1
kmoose
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Outboard Adjustment Training Day

I’m still getting used to my new/old boat but after getting a few trips in it under my belt I was ready to start evaluating ways to squeeze all I could from an already outstanding set up. I was getting over the flu and could not stand seeing my boat sit under the shed on such a nice weekend so I decided to make some adjustments to my outboard mounting height and give her a good test drive.

So what drove me to come to the conclusion that I needed to do anything at all to my set up? Like I said, I had made several trips with this boat and loaded her down pretty well. I’ve had it out on both flat days and ridiculously rough and saw that there might be room for some improvements. Here are some key indicators:

• No matter what speed, angle, turn or seas, I couldn’t make the prop “blow out” or cavitate.
• The cavitation plate on the motor is well below the running surface of the water behind the transom regardless of speed.
• Motor needed excessive trim angle to gain desired attitude.


Under many standard outboard mounting applications, the motor is mounted with the cavitation plate parallel, if not just above the horizontal line that is the very bottom center of the hull. This rule generally will get you close to where the outboard needs to be, but changes in modern hull design have changed this and needs to be considered prior to mounting an outboard on a new or re-power installation. Some of the factors that might require a higher mounting height are notched transoms, integrated platform mounts, hull extensions, or brackets. In my case, the boat was retrofitted with a 36” bracket to a hull originally designed for use with an I/O. The 36” setback allowed “clean” un-aerated water to rise up well beyond the bottom line of the hull, thus allowing a much higher mounting height.

My first course of action was to evaluate where my motor is at and how far I am able to move the motor up without modification. I did this by placing a strait edge against the bottom of the hull out to the lower unit. Then I trimmed the motor so as the output shaft was parallel to the strait edge. My cavitation plate was 5/8 of and inch above the parallel bottom of the boat. I opted to move my motor to the highest possible position ( a one and 5/8 inch raise). So what brought me to this decision? Well, the move was a choice of the last 2 adjustment holes and I choose to go the max and work from there.

The adjustment process was rather easy for the fact my buddy had an H frame lift on wheels…….good to have friends with expensive tools. The end result seemed as a total win, win. Fuel economy was a gain but little to no speed increase. My daughter and I ran the boat through it paces and still could not cause a cavitation or blow out under reasonable trim. From the pics it is hard to tell but in channel conditions I was able to maintain 3 nmph at 30 knots!!! This all felt good and I was ecstatic with the fuel burn…….but what will happen under a full dive load and real gulf seas?
A couple of weeks later the opportunity arose for a trip in 2-4 decreasing all day. Ahhhh the perfect test of the new prop and motor height. So I loaded up the sled with 3 other guys, 400 lbs. of ice, ten tanks and all the associated gear and headed out 50 nautical.

The ride out seemed to go well and I didn’t need near the usual amount of tab to keep the bow down. Fuel burn didn’t seem to be noticeably better. With a lot of throttle tending we made our destination through some uncomfortably spaced 2-3 footers and had a good day of shooting. NOAA was spot on for their forecast for once and the seas laid out to nearly pond conditions. These were the conditions I felt that I would show the fruits of my labor. Unfortunately, as soon as I started to trim the boat up for max speed and fuel burn I started to see some needle bounce on my tach. It was obvious I had lost my ability to trim the bow up under dive load and had actually hurt my cruise speed and fuel burn due to the fact I could not utilize my trim angle to lift my hull out of the water.

So where am I at and where will I go now? I am going to invest into lowering the motor down one hole, (half the distance of the raise) and retest. What will I gain? Who knows, but if I go back to the original set up………which may have been perfect!.......I will never know unless I do it. So this weekend I will move it and hope for the best. I have a good test co-pilot and it beats a day at the mall or pressure washing the pool deck.
To be continued……..
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Old 11-14-2006, 08:52 PM   #2
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Re: Outboard Adjustment Training Day

Try shimming the motor with angled shims, that may help.

If the cavitaion plate is not above the water when you are running, the motor is too low, and will hurt fuel economy.
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Old 11-14-2006, 09:03 PM   #3
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Re: Outboard Adjustment Training Day

"Trial and error" must be the mantra for boating.

I just went through that with my propeller with multiple haul outs and adjustments to the prop until we got it right.
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Old 11-14-2006, 09:06 PM   #4
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Re: Outboard Adjustment Training Day

Quote:
Originally Posted by SpearMax
"Trial and error" must be the mantra for boating. I just went through that with my propeller with multiple haul outs and adjustments to the prop until we got it right.

"Trial and error" may be for us, but Kenny fixing shit that Kenny "Moosed" is another story.

Do a search for a post of him loading a speargun, with a super short, super tight bands, your ballz will never feel the same.
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Old 11-14-2006, 09:12 PM   #5
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Re: Outboard Adjustment Training Day

Hey Moose,

The proper name for it is Anti-ventilalation plate. Ventilation is the prop sucking air. Like if you over trim it,you're revs go up(blow out) with no increase in performance. Cavitation is the "boiling" of water on the prop blades. Anywyas, What hole is it on? What hull are you runnin? What prop/ size are you runnin? What rpm's are you turning? What length motor? (20,25,30)I have seen this problem before and sometimes there no real way to make improvements. Putting a bracket on a hull that it wasn't designed for doesnt always work as good as intended. My buddy put a bracket on his 23 Monza and hung a 300X on it. we tried everything and we could only get it to run mid 50's. At the same time my other buddy with a 21 Formula put a bracket AND a jackplate w/a Yammy 200 and runs 67. My 17' Action with 5" of setback,and a 225 JohnnyRude now runs 94 with a 30 Lightning ET. It's all about set up. Another thing to consider is what kind of gains are you lookin for?? Are they realistic? Sounds like you're pretty close, good luck. Shimming the motor will not help this.
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Old 11-14-2006, 09:18 PM   #6
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Re: Outboard Adjustment Training Day

Kenny,
Rule of thumb is for every inch your outboard is away from the transom it needs to rasied an inch.This works great for performance guys but does little for us.A dive boat could be 3000lbs heavier on a dive day and normal for the family outing.
I need to know what pitch and style of prop you have to offer an opionion though.

Last edited by chasintail; 11-14-2006 at 09:29 PM.
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Old 11-14-2006, 09:24 PM   #7
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Re: Outboard Adjustment Training Day

Every hull is different, so there is no rule of thumb.
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Old 11-14-2006, 09:28 PM   #8
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Re: Outboard Adjustment Training Day

Quote:
Originally Posted by FREEK
Every hull is different, so there is no rule of thumb.

Thanks for the update.
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Old 11-14-2006, 09:32 PM   #9
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Re: Outboard Adjustment Training Day

Quote:
Originally Posted by chasintail
Kenny,
Rule of thumb is for every inch your outboard is away from the transom it needs to rasied an inch.This works great for performance guys but does little for us.A dive boat could be 3000lbs heavier on a dive day and normal for the family outing.
I need to know what pitch and style of prop you have to offer an opionion though.
I thought that it was for every 12 inches, you would raise it an inch.

My bracket has a 30" setback, so we started off with it 2.5" higher.

If I followed your rule of thumb, it would be raised 30 inches, i don't think the prop would get much bite in the water.
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Old 11-14-2006, 09:35 PM   #10
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Re: Outboard Adjustment Training Day

Quote:
Originally Posted by bgbill
I thought that it was for every 12 inches, you would raise it an inch.

My bracket has a 30" setback, so we started off with it 2.5" higher.

If I followed your rule of thumb, it would be raised 30 inches, i don't think the prop would get much bite in the water.


I think he is talking about an airboat.!


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Old 11-14-2006, 09:43 PM   #11
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Re: Outboard Adjustment Training Day

Quote:
Originally Posted by dagodiver
I think he is talking about an airboat.!


Dago.
Exactly.
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Old 11-14-2006, 09:58 PM   #12
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Re: Outboard Adjustment Training Day

Sorry for the typo.Its one foot away to one inch lift.You should be in good hands with all the talent posting here.
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Old 11-15-2006, 07:55 AM   #13
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Re: Outboard Adjustment Training Day

"oooo my god...!!!"
Like some radio show bit would say
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Old 11-15-2006, 08:34 AM   #14
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Re: Outboard Adjustment Training Day

Kenny.... Stop F_cking with Sh_t before you break something!

When you get the engine raised one hole, we can run it in that fresh water lake up by your house.
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Old 11-19-2006, 01:21 PM   #15
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Re: Outboard Adjustment Training Day

Kenny,
Let us know how your adjustment works out. I have the same motor on a 23' Parker with factory installed Stainless Marine outboard motor bracket. The boat came with a 225hp Yammie and the set-up from the factory caused the prop the ventilate quit a bit. Load the tach would "bounce' plus one could hear it since the Yammie was a loud a** 2-stroke. When I repowered the dealer mounted the Zuke the same way the Yammie was mounted, i.e. same hole on the bracket. Im getting much the same results youe were, reasonably good gas mileage (about twice as good as the Yammie) and NO prop cavitation or ventilation.Also when running on plane there is a large "V" pattern of water above the anti-caviation plate that looks as if it would add alot of drag as the boat moves through the water. Regardless how far I trimmed the motor, it would'nt "blow the prop out". Anyway Im thinking of raising the motor 1 hole at time and experimenting. I guess I better buy alot of marine caulk huh?
I'll try to attach a picture.
-Thanks
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