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ContinuousWave: Whaler Performance
2001 18' Dauntless: Mounting Honda 130
|Author||Topic: 2001 18' Dauntless: Mounting Honda 130|
posted 07-28-2014 12:19 PM ET (US)
Hi Gang. I've been posting about steering problems I've had and was hoping to fix. I've gotten some great feedback, but it looks like I'll be replacing the assembly and also the steering tube, which has created the need to lift the motor off the transom.
Since the motor will be off, I had my mechanic look at the mounting plate and if we should move it while the motor will be off. He took one look at where the hull changes to the cavity on the stern and drew a somewhat straight line to the motor shaft. The line came up to the second plainer plate on the motor, which he then said, he would have no hesitation to mount the motor as high as possible (i.e., mounted to the lowest bolt hole) to minimize drag.
Does anyone have any experience with their motor being mounted here? What kind of performance changes can I expect? My initial thought was higher end speed by reducing drag, but now I'm worrying about having increased difficulty getting on plane since the propeller will be closer to the surface, decreasing the angle at which the prop will push the boat out of the hole putting making it harder to get on plane. My other train of thought: if the angle is decreased, and the propeller is closer to the bottom of the hull, the bow will be lower and the stern higher creating less drag during take off.
If anyone has a clear thought or similar experience, this would be a big help before I start messing with my motor mount location.
Thanks ahead of time!
posted 07-28-2014 03:43 PM ET (US)
I don't recognize "the second plainer plate on the motor" as an identifiable location. An outboard engine will typically have a large anti-ventilation plate that is located just above the propeller aperture on the gear case. Above the anti-ventilation plate there can be smaller spray deflector plates.
The benchmark for locating the engine mounting height is the anti-ventilation plate. Even if you meant to refer to one of the spray deflector plates by your description " the second plainer plate", it would be of no value as a location because there is no standard for the distance between the anti-ventilation plate and any spray deflectors. On your engine the spray deflector might be six inches above the anti-ventilation plate. No one knows where this would put the anti-ventilation plate.
The desired position is for the anti-ventilation plate to be running just at the water surface or even just above the water surface when the boat is running on plane at a fast cruising speed and the engine is properly trimmed. It is not particularly important what the relationship is to a line projected aft from the hull, although it will almost always be well above that line.
If the anti-ventilation plate runs submerged when the boat is on plane at fast cruising speed with the engine trimmed, the general notion is the engine mounting height is lower than necessary.
Exactly how high a particular outboard engine can be mounted on a particular boat is best determined by experimentation. The boat hull, the outboard gear case, and the propeller in use will affect the outcome.
The measurement of engine mounting height is in units of 0.75-inch or "holes" relative to the lowest position. If an engine is mounted as low as possible it is in the lowest position. If the engine is raised one set of holes, it is then "one hole up." Raised two sets of holes, it is "two holes up." Most engines have only four sets of holes, so "three holes up" is typically as high as possible.
posted 07-28-2014 03:54 PM ET (US)
Jimh - As always, thank you for your input and sharing your knowledge. My apologies for using incorrect terminology. I guess it is a testament to your knowledge that you were able to dissect my post accurately.
So, I believe my motor is mounted "one hole up" and I'm sure by mounting it all the way (actually there's 4 holes) 4 holes up, the anti-ventilation plate will still be below the water surface while at fast cruising speed.
I am very eager to see how the boat will perform with this change (and a new smooth new steering mechanism). I will report the results when the work is completed and I'm able to effectively test.
posted 07-28-2014 08:41 PM ET (US)
If there are four sets of mounting holes, you can only mount "three holes up". Again, the engine height is measure from the lowest position. The lowest position uses one set of holes. That leaves three sets for the "holes up" mounting.
Before you take off the outboard engine, go for a run and observe where the anti-ventilation plate is running relative to the water surface. Look at the images in this article
A-V Plate Pictures
for some guidance.
posted 07-28-2014 09:38 PM ET (US)
I have the engine mounted all the way up on my hull, and I will probably lower it one set of holes. I have tested seven different styles of props this year, including four blades, and all of them will ventilate at a certain point if I try.
If you mount it too high the prop will ventilate in tight turns and possibly when getting on plane.
I like to have my engines mounted high, but I am just a little too high I have found. You may be able to run all the way up, but be prepared to lower one bolt hole if necessary.
Your mechanic is right that you are probably a little too low right now, and will probably see a slight benefit from raising the motor. To gain all the benefits possible though you will need to experiment with different props.
What is your current prop now?
posted 07-29-2014 11:18 AM ET (US)
Thanks for info - I guess I'll go with three holes up and test that out. I should hedge my expectations a little bit by the sounds of it. Right now I'm running a Honda SS 3 blade 13 1/4 x 15 prop. The boat handles pretty good in terms of top speed, getting about 38-40 with myself and just under a half tank. The hole shot isn't the best it could be, but I'm attributing that to the design of the boat (beamy) and a heavy motor (505lbs). If there is more than my wife and dog behind the RPS seat, the boat seems to delay a bit in getting on plane.
I was really hoping that moving the motor up would help my boat get on plane. Any idea on whether this will effect the boats planing ability by just changing motor height and NOT changing the prop?
posted 07-29-2014 07:19 PM ET (US)
The Honda 130 is a heavy motor and not known for being a powerhouse. Raising the motor will help top speed and maybe a little better economy butI ccan't guarantee much improvement in hole shot.
Your prop is pretty dinky at only having 13" of diameter. You need to try a prop with around 14.5" diameter or a four blade prop for better hole shot and I would still raise the motor.
I dont know Honda props but a Stiletto prop may be a good place to start.
posted 08-05-2014 09:08 AM ET (US)
Hey Guys - Just put the boat back in the water yesterday. First off - new sea star cylinder and trim pivot pin and steering tube has made a huge difference - expensive maintenance work, but well worth it.
Second - the motor was lifted to the third hole or in other words, all the way up. I do notice a slightly faster WOT speed at around 43 mph (GPS speed) at 5600 rpm. I also noticed slightly less bow rise coming out of hole and seems to plane slightly faster.
My mechanic doesn't seem to think re-propping will benefit much since I'm getting WOT in the range where I want to be and hole shot isn't too bad.
If by putting on a larger prop (14" stilleto) with the same pitch (15") - what should I expect in terms of performance? Faster hole shot with less WOT speed? or should I expect better performance overall?
I'm also considering adding a stingray drill-less hydro foil, but I'm still on the fence on this. I'm just looking to optimize performance of the boat and make it the most enjoyable to drive as possible.
posted 08-05-2014 10:10 AM ET (US)
I can't offer any advice on an optimum propeller for your application. I'm not sure what you want to accomplish. Your speed at WOT seems appropriate for your somewhat heavy boat and motor. I'll assume you want to improve hole shot and lower speed performance on plane.
A hydro plane stabilizer may be helpful since you've raised the engine and the anti-ventilation plate is almost certainly above the water while on plane thus eliminating the on plane drag of a stabilizer. You may also try lowering your engine one hole.
Before proceeding I would hope you can get a recommendation from Tom Clark. If he does not see your post you can send him an email. In my experience his recommendations are extremely useful.
posted 08-05-2014 11:41 AM ET (US)
"the motor was lifted to the third hole or in other words..."
Matty--please describe the mounting height of the engine using units of "holes" or 0.75-inch and give the height in reference to the lowest position. If you do this you will remove all the ambiguity and you won't need to describe the mounting position two or three different ways.
Do you mean you have the engine mounted three-holes up?
posted 08-05-2014 11:45 AM ET (US)
"...by putting on a larger prop (14" stilleto) with the same pitch (15") - what should I expect in terms of performance?"
In general, if two propellers have the same pitch, the one with the larger diameter will be harder for the engine to turn. This means the engine load will be greater. In general, an engine with a greater load will accelerate more slowly than if it had a lighter load.
These are general rules of physics. Exactly how two propellers of different diameters, made by different manufacturers or of different design, but having the same rated pitch will perform on your boat, with your engine, under your testing conditions will be hard to predict.
posted 08-05-2014 02:42 PM ET (US)
Jimh - Excuse my ambiguity - but the motor height confuses me - quit frankly.
As you say it - I have the motor mounted three holes up.
Also - thank you for the basic physics lesson - that was exactly the kind of theoretical information I was looking for - much appreciated. I believe I'll keep my current prop. Personally, I feel the motor is loaded plenty when trying to get on plane, maybe too much, but that is just a "feeling".
If I decide to put a hydrofoil on, I will post the test results. Thanks again for the thoughts and wisdom.
posted 08-05-2014 03:53 PM ET (US)
43 MPH with a 500 pound Honda 130HP on a 18' Dauntless sounds great.
Here is a link with a couple of posts from you and your rig.
posted 08-05-2014 08:44 PM ET (US)
Matty says: "...I have the motor mounted three holes up."
If the engine mounting bracket only has four sets of holes, then at three-holes-up you have mounted the engine as high as possible with that mounting bracket. Note that there are some engines with mounting brackets with five sets of holes. On those engine you could reach four-holes up as the highest position. Generally you see the five-hole mounting brackets on Mercury engines only.
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