Which prop (3 or 4-blade) for a 18.5 ft Alicraft 18 Norwind with Mariner 90 2T

[GreedyMuffin]

I am only using Mercury props. 13x19 and 13 3/4 x 15.

My sea-level is normal. 0 meters.

I am not trolling often. Just general usage really. Daycrusing with friends.

 

[walleyehed]

Which holes are being used for eng. mounting? Is the outboard literally setting all the way down "On" the transom lip?

 

[GreedyMuffin]

Hello!

I do not remember, but the engine does not rest on the transom. It is about 2-3 CM over. So it should be optimal-ish? The plate on the gearhouse is 1 cm over the bottom of the boat at least.

 

[Sea Rider]

Can't possibly tell if OB sits on ideal transom height or not if don't know what's going on at back of lower leg, for that need to pull head out transom while on a wot run on calm water. Can play with OB heights afterwords. This example illustrates well the difference of a badly height seated OB and a opt seated one.

http://forums.iboats.com/forum/gener...x-return/page2

Try to match second pic example on "post 23" on your combo, will love boating with that setting once dialed.

Happy Boating

 

[walleyehed]

That's a random, ball-park way to start with. I have to disagree with it being optimal as the prop design will set the allowance for how high the engine can be run.
That's a good starting point but not an "optimal" point. That may be it for a std, run-of-the mill set-up. My plate on my Lund is 3" above the water line at WOT. It's what the prop will allow.
On any "V" hull with no pad, lower eng. to level, boat on trailer. Lay a 2x4 or straight edge of some sort on bottom at keel, trim av plate to parallel. With it there, measure back from bottom point at keel to front of/L.E. of gearcase, for every 7" back you want av plate 1/2" higher. so if it's 16" back, av plate should be close to 1" above boat bottom.

 

[GreedyMuffin]

No Title

searider The engine is like your picture number two. I have checked it. It seems to be a decent height at least.

This is screenshotet from a video I had, so excuse the poor quality.

I can take a better picture from behind once I get the opportunity to test the boat again.

Again, thank you all for your help!

"On any "V" hull with no pad, lower eng. to level, boat on trailer. Lay a 2x4 or straight edge of some sort on bottom at keel, trim av plate to parallel. With it there, measure back from bottom point at keel to front of/L.E. of gearcase, for every 7" back you want av plate 1/2" higher. so if it's 16" back, av plate should be close to 1" above boat bottom."


My boat got some sort of keel in the front, but stops. (see picture in link, it is only google drive, no need for download or etc.)

With no pad? Can you explain a bit further to me? I understand everything until the marked area. Do you mean inches, or cm?

Link for google drive photo album: https://photos.google.com/share/AF1...?key=LXhrWlJHelFSNnZzRFQzZ3g0NUxVV0xfVHRzVmdB

Thank you all again! Sorry for any inconveniences I might have started due to my lack of English understanding.

 

[Sea Rider]

Sorry to disagree too, it's not a ball park to start with, its a ball park to end with, standard props factory delivered likes running that way, clever ones doesn't. That setting works spot-on on flat, choppy, windy water cond, not extreme though and at tight close dime turns without prop areation.

The sissue with this setting is that nobody cares about too much work, prefer playing with trim, moving OB up-down without checking what's going behind lower leg. Works very well with newer OB's that has 2-2.5 inches lenght from upper deflector plate to AV plate. Boaters that have tried that setting are very pleased with it and boating happily.

Bottom Line : Each one with its own madness..

Happy Boating

 

[GreedyMuffin]

If I trim too much in, the nose goes down and the boat handles very poorly, water everywhere out the sides etc. If too long out, it sounds to start sucking air, but I am not certain.

 

[walleyehed]

Greedy, what you describe says you are very close to optimum height for the prop installed.

 

[Sea Rider]

Greedy, what you describe says you are very close to optimum height for the prop installed.

Yep, we're talking about recreational/family leisure boats, not speed demon ones which uses different OB heights & props for that kind of boating. Bear in mind that each boat has a unique OB installation, not all has same transom heights nor OB brands have same lower leg lengths, this hanky panky could result in a mediocre combo performance if in pursuit of boating perfection specially if running underpowered OB's.

Happy Boating

 

[Sea Rider]

If I trim too much in, the nose goes down and the boat handles very poorly, water everywhere out the sides etc. If too long out, it sounds to start sucking air, but I am not certain.

With deck weight evenly distributed. Ideal trim is the one that makes hull, prop shaft & AV plate to ride parallel to water level once on plane. If having water splashes over transom or prop areation on choopy sea cond and at tight close turns you have a badly height seated OB on transom that must be looked after if wanting full fun out of your combo.

Happy Boating

 

[walleyehed]

All due respect, Sea Rider, have you ever messed with this?? So-so performance is not acceptable to me. I have go-fast and many "normal" rigs. Set it up for best efficiency, period. No excuse for poor performance because you are unwilling to optimize the setup. Read "performance" as proper operation not speed. I've been doing this for 38yrs now on a large-scale fashion, it works and there is a whole lot more to making a boat act as it should than just bolt the engine on and go..That's just Standard and no better than standard. I strive for more, as I've found what works and what doesn't. In this case it's up to the customer to decide what they want.. Standard, generic set-up or something that will be better than average.

 

[Sea Rider]

Walleyehead,

You have just hit the nail, plain in agreement with your post. Performance to me it's the overall good operation of the combo in terms of excellent hole shot, good rpm/speed increase throughout the entire throttle range provided that OB revs at it's max wot rpm range as usually loaded.

There are different type of boaters, the ones that contents to hang an OB on transom and go boting with, don't know anything about hole shot, lugging/over revving an engine, props, etc.

Ther are the ones that likes doing certain things to slight better combo performance, and finally the skilled ones that likes going for top water performance usually playing with OB heights and installing tachs to maximize prop revs..

It's all down to which categorie of boater you are...

Happy Boating

 

[GreedyMuffin]

Hi!

I just bought an 17P. Sold a second 19P as well. Now I have 15, 17 and 19P.

The 15P gave too much RPM, 19P was a little low. So recon that the 17P will be perfect!

I will experiement with the height, but I think it is pretty good. When running on plane, no water were splashing out the sides. It was pretty dry and nice.

Will post a picture once I get the new prop installed. Will also check the carbs, that they are pushed out correctly. This prop sat on a 19ft Jeep with a Mariner 90 from 2001, a four-stroke though, and not a two-stroke that I have.

 

[Sea Rider]

Were those prop water test done with a tach ? There will always be some kind of water splashes side of hull which is normall, meant water splashes front of lower leg towards transom or over transom. Is middle wake flat out ?

Happy Boating

 

[GreedyMuffin]

Yes. Got 5000-5100 with 19P, and 5900-6000 with 15P. So I reckon that the 17P will be somewhere around 5500-5600 - Which is fine. I will check the carbs as well. If they are 100% open. They should, but I do not know yet. Will find out soon!

https://www.finn.no/bap/forsale/ad.h...6&fks=94660286

The ad for the prop. Payed about 35 USD + 20 USD in shipping. A new prop cost 210 USD + shipping. :-O

Will check after school today if the carbs are opening correctly. WIll post pictures and/or video if I take it out for a test.

If I trim out too much, it sounds like it is sucking air, and the RPM can go up to 100-200 RPM. When I notice that, I always take it a bit in so the RPM decrease to the "normal".

 

[Texasmark]

If I trim out too much, it sounds like it is sucking air, and the RPM can go up to 100-200 RPM. When I notice that, I always take it a bit in so the RPM decrease to the "normal".

That's what I call the sweet spot. For that setup/prop/engine/boat combination, you are getting all you can out of it when you do what you did.

 

[Sea Rider]

If wot range for that OB is 5000-5500 rpm, with 19 pitch OB is on the extreme lugging side, with 15 pitch is over revving badly, so 17 should work around middle of both previous 2 pitches.

One thing that don't understand is, why do you need to play with trim constantly. For "recreational" boating hull, prop shaft, AV plate should ride parallel to water level at plane, that's achieved when OB sits at 90?on transom, usually 0 trim position. That's mentioned on every OB Owner's Manual that have read, is not an invention of mine as one could wrongly suppose..

Don't know if your combo is easy or hard to plane. Try 1 trim up position while resting on water, go full hammer down, should achieve slight bow up, once on plane, set trim to 0 for combo tu run as stated previously. Deck weight should be well distributed for that to happen nicely.

Happy Boating

 

[GreedyMuffin]

Hi!

Yeah. That is what I seem to find as well. 15P is too much, 19P is too low. The 17P was at a great price as well!

The carbs are opening correctly. Could just barley move them a tiny bit. Nothing noticeable though.So I think we can clear them.

The boat goes on the plane very easily. With the 15P it was on full plane from neutral/idle within 3 seconds!! With the 19P it went from 3, to 7 secs. So with the 17P, at least 5 sec.

About the trim, I do not know.

I can possibly try to change the height on the engine a bit. Move it up perhaps? Or should I keep it as it is? I just do not want to run it particularly higher due to the reason it might "suck" air more easily when turning. I have noticed that when I turn, the prop is perfect when under "normal" trim. If I turn very hard, the boat "slides" a bit, but I guess that is the boat design. I have only tested once, can not confirm as of yet.

Is it normal that the RPM goes up when it is too far trimmed out? When it is trimmed out too much, the engine is no longer parallel with the surface of the water. When as good as it gets to parallel with the water, the engine is under the "normal" state. That is around 5000 RPM under WOT.

Sorry for asking "dumb" but I learn that way to get a confirmation on my way of thinking.

This weekend, I will try to test 5 or 6 people n the boat WITH the 17P. I do not want to run it too much more on either the 15P or 19P. I might keep the 19P as a backup prop just in case. Since it will work, but the 15P will not at all due to the badly over-reving.

Thank you all very, very much!

 

[Sea Rider]

Let?s do some ABC experimentation?

Let's suppose that your OB has manual trim, so set it to 90?, that's perpendicular to water level as in pic.

Distribute deck weight evenly..



Make a wot test as indicated and check if prop aerates on close turns on calm water cond. If not, height is ok, assuming that there's no water splashes towards transom or over it which is no bueno to have as will slow combo down due to lower leg achieving more unwanted drag.

The only way of knowing if OB sits at the sweet transom height is by visual over transom inspection to "determine" which is key if prop is doing it's homework right. Type, size, OB-HP doesn't matter since it's a matter of individual set up adequacy as all are unique.



By visual inspection will know if OB needs to be raised or be lower a bit. Raising is easy, lowering is a PITA if already sitting on top upper transom.. All other forms of water experiementation dialing sweet OB height are just useless wild guesses while losing precious spot on boating.

Ideal height for recreational purposes is as in pic, achieves nice hole shot, fast plane, no prop areation at tight close turns, all these at wot speed. Max fun is fully guaranteed..



Try it , report if water performance bettered, combo seems to just need fine tunning a bit actual configuration..

Happy Boating