2005 Honda 90 - which prop?

M

Major Tom

New member
Hi, I need to get a spare prop, and while I'm at it I thought I might experiment with a slightly different pitch or diameter. I've read several posts on this subject, but could use some advice specific to my situation.
I just got this boat, changed oil, new plugs (the recommend NKGs) and took her out twice. The previous owner painted the prop blades (not the hub) with bottom paint, and she has decent bottom paint but needs a little touching up. I ran her light, with just 20 gal of gas total, no gear, 125' of chain rode in the bow, and 350 lbs of skipper and first mate. Prop is stock Honda 3 blade 13.5 x15 aluminum.

WOT I get 5200 rpm, 28 mph gps over ground, on flat water.
I'm also using 93 oct non-ethanol gas, Techron Fuel sytem cleaner, and a touch of Stabil for good measure (about 50% of maintenance dose). After I run a few more gallons of that through her I'll use some Seafoam and see how that does. She ran smooth through the entire range, but idles a bit low, around 650 rpm.

Those results are OK, but from what others have posted and the specs on boat test I thought I'd get around 5500-5800 and top out at 30-32 mph. I've used Techron on other engines, and I usually notice a slight drop in performance until I put fresh gas in her. So maybe it's that?

My main concern isn't eeking out a couple more mph or mpg, (although a bit more top end speed would be nice ) but I do want to ensure that everything is tuned as it should be, and that the motor and carbs are clean. I'm waiting for my outboard mechanic to look her over so that's why I'm posting this. (he's so busy now I can barely get him to return calls!) I haven't added a kicker yet either. Not ready to have carbs cleaned, too many other mods and rigging to do now, and my mechanic is so backed up anyway...will probably do that next spring.

Any suggestions? I thought about trying a 14 x15 or 14.5 x 15 if I can find it. But that would lower my rpms, and I don't think I'd get any more top end speed. So maybe i should go the other way and try a bit less pitch, like a 13.5 x 14? BTW, definitely aluminum... I plan on boating in a lot of unfamiliar waters :mrgreen:

Thanks!
 
I have a different boat, different motor, different props, etc., so I (and likely nobody else) don't have the exact information you need. When I did prop research, I found everything is based in generalities. Basically, you pay your money and you take your chances. But some of my experience may apply.

I had a 3 blade aluminum 12" pitch prop that came as original. WOT was 5,200. That was on the low end of acceptable for my motor. For my spare prop, I wanted to go with less pitch to get the rpms up. Also, if I boated at higher altitudes than sea level, I needed less pitch.

But there were other considerations. First, the boat squatted in the rear because of extra weight (common). A 4 bladed prop is supposed to lift the stern. Second, 4 bladed props had a better reputation for handling at low speeds. I planned on (and have been doing) a lot of low speed handling in tight places.

Going from 3 to 4 blade, and a change of pitch, and moving the gas tank, and moving both batteries, and lifting the engine one inch, and adding a permatrim, made my calculation complex. Calculation might be an overstatement. It made my guesstimate more complex. I went with a 4 blade 10 pitch, using a common rule of thumb that an extra blade will drop WOT rpm 100 and an inch less pitch will raise rpm 100.

I got what I wanted with WOT at 5300. Top speed may have dropped 1 mph, but top speed wasn't my concern (if it was, I'd stay with a 3 blade prop). The benefits are that my early calculations show that the normal cruising speed is more efficient. Fast idle (1000 rpm) speeds are improved at the same rpm, and that's a real comfortable and efficient speed for looking at stuff. I probably spend more than half of my cruising time at this rpm. The grip of the 4 blade is noticeably improved when maneuvering at the dock.

My new prop used a different hub system, so I bought a spare 4 blade and sold the original 3 blade. Here is where things went sideways a bit. Because my rpms were still on the low end for the motor, I went with a 4 blade 8 inch pitch. Running that prop got me a few 100 more rpms with a small gain in speed. But the stern was lifted too much. I had some cavitation streaks on the prop where the epoxy coating was pulled off of the prop surface. That's too complex to cover here, but basically when I made a sharp turn (which I don't generally do) I could hear air enter under the ventilation plate (so it might be more accurately called ventilation streaking).

I think that the easiest solution, for me, is to lower the engine back down an inch. I got what I wanted when balancing the boat, but the motor is no longer too low when running a 4 blade prop and with 250# moved out of the stern.

Since a request for prop sizing is a request that people make a guess, I'd say go with the same diameter and two inches less pitch, especially if you are looking for a spare to boat at altitude.

Mark
 
Like Mark, I will steer you with what we learned on our 19 angler.

We run a heavily loaded 19 angler with a 2003 Honda 75. We started with a 4 blade aluminum 13 inch 15 pitch prop and it worked ok before we started really loading it up. The planing ability and general response at sea level was OK but we knew it would struggle at higher elevations and our increasing load at the time. I wanted to try a 13x14 but had trouble actually finding such a prop for our motor. So....

We switched to an aluminum 4 blade 13.25 inch 13 pitch prop last summer thinking the increase in diameter would compensate some for the 2 digit pitch drop.

It has been working great and is now our main prop. We lost about 2.5mph of top speed but the planing is now more effortless, responsiveness to throttle changes, more immediate, and our cruising speed of 14-16 knots still keep the RPM under 5k unless we get needy.

We run the boat about as heavy as your average 22 cruiser but have a little less hull to push.

Greg
 
The 13.5 x 15 is the stock prop, and many boats get up to 6,000 RPM with that. I do with my 2006, when light--and the boats should be nearly identical, since I have the same motor. I do have bottom paint, but it is in very good condition. I also have a foil, and trim tabs. It is possible that your motor is too deep (set too low on the transom). This is common with the C Dory and Honda, The anti ventilation plate should run right at the surface of the water. (not below it).

You are probably not going to find any 14" pitch props--just rarely made--although you can re pitch a 15. You would like to turn up at over 5500, preferably 5800 to 6000 RPM WOT.

To go with an aluminum prop, you probably would be best with a 14 x 13" prop. That happens to be the one I use at Lake Powell. (3700 feet, loaded boat) I also have a 14 x 11, which I can use at Powell, or higher elevation.

No reason to run "Stabil" unless you are not burning that gas in a month. During cruises or times I am running the boat regularly, I don't put any Stabil in the fuel--does not add anythings. Many suggest running "ring Free" by Yamaha. One of our dealers suggests against Sea Foam. I do run a carb cleaner with the first tank of fuel I burn after some lay up.

The 650 RPM is OK--but it is easy to turn the idle up slightly. if you want.

Have you played with both engine trim and trim tab alignment to get to best speed (RPM) out of the engine?--the 5200 suggests to me that either the bottom is foul, the boat is not trimmed to the best,or the motor is too low.
 
Thanks for all the ideas. I do have trim tabs, and both tabs and the motor were trimmed optimally... I couldn't get any more rpm or speed at different trims. Trimming the tabs down a bit of course got me on plane better, but with the expected drop in speed of about 1-2 mph.

Hmmm, I'll have to check the motor height, thanks for that, thataway. The bottom paint is OK, but not exactly smooth... there are several spots where you can see the "chips" that flaked off, maybe 3"-4" wide, and then painted over. Just like old house windows or whatever. So I'm sure that's not helping. But there aren't any barnacles or other growth at all. Also, I would think the bottom paint on the prop is a major part of the equation... instead of cutting and sliding through the water, there's a lot of resistance from the bottom paint on there... you can see the brush marks very, very clearly.

Since I don't relish the thought of stripping down all the bottom paint right now and going with Micron or something smoother (need to research that another day), I think I'll focus on the other areas first. The most I ever plan to be in saltwater at dock is maybe 2-4 weeks, once a year. The rest of the time she's on the trailer, and sometimes on a freshwater dock maybe 4-5 days at a stretch, max.

And yeah, I hear you on the Stabil, it more of an insurance. The boat had been layed up since last fall, according to the previous owner.

Which carb cleaner do you use? I know, I've had mixed results with seafoam... one time on a really dirty carb it dislodged some varnish or something and that just clogged the jets further, ended up rebuilding carb anyway. So I think I'll look into that Yam ring free.

Thanks!
 
The aluminum prop is painted? There should be no reason to do that! The lower leg should always be lifted out of the water, after the engine is flushed with fresh water the being run in salt water. It is very possible that the prop has been dinged up, or even out of balance--although that would probably show up as vibration.

At the least I would use one of the paint strippers and get any bottom paint off the prop. File any dings, sand the prop smooth. (best to have it balanced by a prop scan) You can then spray paint (cans) primer, and proper paint, or even a thin coat of one of the bottom paints designed for props. (One of my boats, I cannot the the nose of the lower unit cone fully out of the water, so I spray it with a light coat of bottom paint for aluminum.)

I use "Gumout" carb cleaner, only when there is some question about leaving ethanol laced fuel in the system. I am not sure it does any good, but I have filled the carb bowls up with it, when I couldn't tear the Honda 90 down to properly clean the carbs, and it seems to have worked. . Seafoam: I have been working on outboards/running them for over 65 years---and never used Seafoam, with a couple exceptions. Yes, I know that lots of folks swear by the stuff. There are a lot of "snake oils" in fuel/oil additives, They make smoke, etc, and rarely are needed. Nothing magical: pale oil, naphtha, and Isopropyl Alcohol. That is it.

If the bottom is rough, this may create some of the issues.

Another whole potential is that the tach may be off. First be sure that there is no corrosion anywhere on the ignition or tach wiring. The RPM could be verified by using a direct tach on the flywheel to check it out, or use one of the small tach, which are surface mount or induction (around the spark plug wire)

Here is instruction for trouble shooting tachs. The last section applies to the Honda tach, Telefex is very similar to the Honda Tach.

The reason to be suspicious of the tach, is that the MPH (assume that this was GPS in no current), is pretty close to what one would expect--and the 2 mph are easily attributed to bottom paint.

If you are always going to boat with a light load, then a 13 1/2 x 15 would be the proper spare--which is what you should currently have. (unless it has been altered, or bent--and repaired). At sea level or most places If you are going to be at over 3500 get, then 14 x 13.
 
Thanks, Thataway... you are so helpful :D

Yeah, I don't know why it's painted, maybe it was repaired. I got the impression she stayed docked a lot. But as far as I can tell by simply running the prop is very smooth, no vibration. I'm going to take her out today and check height, I think you're right on the money about that.

I never had much luck painting, even on the couple of times I had a prop professionally repaired and painted the paint always started to flake off... that's a lot of hydro friction.

You've given me pause on the seafoam... I agree that it's hit or miss. I think if it's just mildly dirty it works well, but if you have a lot of varnish or other residuals it can make things worse. I did use it on a Merc 90 after I'd bought it used, well maintained... although I didn't have any significant carb issues, afterward she did start better, always on the first crank of the piston, and seemed to run a tad smoother overall. And good point on the tach, I'll check that too.

Anyway, I have so many things I want to do to get her fitted out the way I want! So right now it's one thing at a time... I'll see how the height is and go from there.

It's been so calm lately, I also haven't had a chance to try her in some rough water (unfortunately around here on the lakes the most we get are only about 3-4 footers on lakes in heavy winds). For some strange reason I've always loved being out in weather, on a boat that can easily handle it. So can't wait to put her through her paces.
Thanks!
 
I checked the height yesterday, it's definitely too low, I couldn't see the AV plate.

With the current mounting I can raise it up 2 more holes, I guess that will give me about 3/4" rise per hole. But, the 2 bottom engine mounting bolts (the ones in the slots) are too low, there's only about 1" left on the slot, so I think I can only go one more hole without sealing the old bottom holes and drilling new ones. I can try going up one hole, and I'll probably do that, but I just don't think it will be enough... I've watched a few videos of moving up one hole at a time, and my best guess is I'll need 2.

How hard is it to re-drill and fill the 2 "slot" holes? Anything special I need to do, other than the standard over-drill/epoxy? Or should I let the local dealer do that? Even though I'm pretty handy, it's a little scary drilling holes in the transom.

Thanks!
 
Try the one hole first. It may be enough. There are other ways, such as a low setback jack plate.

If you fill the hole, it is not all that hard to do. You do want to do a very slight undercut, to get to fresh core, put on un-thined epoxy. I would make an epoxy mixture of glass fibers, cabosil, and high density filler. Let that go off, after packing it tightly in the holes, from both front and back. Then cut 8 circles of glass cloth the first 4,1/2" larger than the hole, and the second 4 1" larger than the hole--grind out slightly the area 1/2" and 1" larger than the hole, inside and out, then put the epoxy/cloth circles in place and finally fair this and gel coat or paint. Some folks would just drive in a wooden dowel coated with epoxy and then fair in, and put a layer of glass/gel coat on the outside--probably almost as good. Must be very tight fitting, and the inside of hole, clean and epoxy coated.
 
Thanks! Yes, I'll try the one hole. And thank you for the detailed isntructions on filling the holes... it doesn't sound too difficult. I need to learn how to do that anyway, given the mods i want to make. Thanks, Thataway!
 
I got a new Amitas prop, same as the old one (with bottom paint!), 13.5 x 15. Tried it out yesterday, and oddly I only got to 5000 RPM. I still havent' raised the engine.

My previous trip with the old prop, I actually got it up to 5400 RPM (I think it was the clean, no additive 93 non-ethanol gas). The lake elevation was about 400'.

I then did some more work on the boat, sanded and bottom painted (same exact paint as before), removed about 100' of chain from the bow (maybe 150 lbs... not good for my back ), and changed to the new prop. Took her to a different lake, elevation 1700'... 5000 RPM. Tried all different trims, etc. Hmmm... would 1200' additional elevation really reduce engine performance that much? Well, one of these days I have to raise her up that one more hole and see what I get. :lol:
 
Update in case it helps someone later:
I raised it one more hole and what a difference. I now get 5500 at 30mph, and that was with a loaded boat with maybe 250 extra lbs... on an unloaded boat I'm sure I'd get 6000. The chain is still out fo the boat and I'll keep it that way. Haven't tried it yet with exactly the same weight as before, but I don't see a need to now.

I could immediately feel the difference, she planes sooner, acceleration is better, and every aspect of performance was dramatically improved. Most important, the AV plate was in perfect position, just barely on top of the water. I could feel that she planed better, too, she just felt "right" and more efficient.

In my case the AV plate is now about 1" ABOVE the keel. Before, when it was even, it just didn't work well.

Many thanks to Bob Austin... he suggested this right off the bat. Thanks!
 
Major Tom,
I have owned three C-Dory 22' cruiser's. Each had a Honda 90 motor and all motors were equipped with "13.5 X 15" props as OEM's. After experimentation using other diameters and pitches, I came back to the OEM. When the boat is "heavy", I do run a 4 blade "13 X 15" that works out well. Best of luck with your "prop pitch adventure"!
 
Spent a lot of time reading threads re: Props.

Found this thread about my motor.

I currently have a 4 blade, 13.25 X 13 prop. Just installed Permatrim but have not yet had it in the water since.

To get the top of the Permatrim near the bottom of the hull I had to raise the motor a lot with the tilt. You can see from this pic that I am 4 holes up in the tilt adjustment bracket with the pin currently in the last one.

IMG_20200621_191142.thumb.jpg


Here is a pic showing the relationship to the Permatrim and the bottom of the hull.



IMG_20200621_191246.thumb.jpg


They are also in our album.

Going to the lake sometime in the next two days and see how she runs.

It seems to me that I should move the lower pin up at least a couple of holes as I don't think I would ever want it trimmed so far down.

Thoughts?

I will let you know WOT RPMS and MPH after we get back rom trying it out.
 
You want the permatrim just at the surface of the water on a plane.

Any trim, is done with the tilt and trim switch on control lever. The pin, is a stop which is normally left in the furthest down position.
 
Nancy & Bud, The "bottom photo" shows the Permatrim to be in the exact position you want it, just slightly below the hull bottom. If it were any further above the hull bottom, cavitation could occur. Moving the adjustment "pin" inboard or out will allow trimming the angle of attack of the boat. Depending on your fore and aft load distribution, you need to experiment with settings. With a 13" diameter prop, you might find that "WOT" can be attained but not optimum speed. Its a trial and error situation until you realize the best settings. Try to do it in calm water!
 
Finally got in the water.

WOT 5400 RPM

Top speed 24 MPH per Garmin GPS

Permatrim made a great difference in getting the bow down.


Smooth water with no wind.

Have 3 blade 13.25 x 15 prop that I will try next.
 
Depending on "drift, current, and wind", a GPS indication of true "speed over ground" is difficult to attain. However, "imperial experience" has produced many examples of what works best for most 22' C-Dory owners. The hydrodynamics involved in choosing the diameter and pitch of a prop are limitless. I personally try to keep engine speed to less than 75% of its rated specification. This has resulted in maintaining durability and fuel management. My suggestions are to continue experimenting giving consideration to vessel loading, and don't deviate too far from the factory standard 13.5 X 15" prop.
 
Going to try the 13.25 x 15 prop next.

You may be confused about speed thru water and speed over ground.

GPS gives speed over ground, regardless of wind, current etc.

A paddle wheel speedometer only measures speed thru water. If I'm going downstream in the Mississippi River with a GPS it will give my actual speed over ground.

If I had a paddle wheel speedometer, it would only show speed thru water and not be able to calculate speed over ground as it doesn't measure current.
 
Back
Top