Another prop question

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bansil
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Another prop question

#1 Post by bansil » Tue Jul 17, 2018 2:47 am

So our top speed is 12 mph @ 5800rpm with a fairly light boat ( need to weigh her) michigan prop recommends Michigan Wheel Vortex 13-7/8" x 11 RH 941411 boat prop.

I have no idea what is on boat now, but damn we are just way too slow, i can drop to cruise rpm about 4600 and it is still 10 mph speed checked with 2 phones and chart plotter

Engine is 1990 2 stroke suzuki DT90...I should be closer to 20 mph right? O
I got past by a pontoon and 6 people last weekend with a 50 merc on back....

urbnsr
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Re: Another prop question

#2 Post by urbnsr » Tue Jul 17, 2018 4:48 am

I have had very good results with Michigan prop suggestions to get to WOT RPM. If you're running a clean prop at 5800 RPM, I would wonder about prop depth from what I have read. Do you get easy blowouts while in a tight turn? If so, I would wonder if the prop isn't deep enough. Otherwise I would suspect too deep. I would think too deep would be more likely, but...

I am just thinking out loud.
Last edited by urbnsr on Tue Jul 17, 2018 6:30 pm, edited 1 time in total.
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bansil
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Re: Another prop question

#3 Post by bansil » Tue Jul 17, 2018 9:19 am

I notice if i trim up even a little bit it gets real loud ,either ehaust ie prop out of water, trimming all the way down does nothing to bow ht or speed.

I hope to get down to boat after work tomorrow and get prop numbers and see how it sits stationary and then compare to under way, engine could be too high which explains trim issue

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bansil
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Re: Another prop question

#4 Post by bansil » Tue Jul 17, 2018 9:22 am

Also to after reread, it may be too high, i get a pretty big rooster tail

Also it will rev higher very easily, i limit it at 10 mph which gives me no over rev.

So more pcs of puzzle, thanks for insight!

urbnsr
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Re: Another prop question

#5 Post by urbnsr » Tue Jul 17, 2018 9:29 am

It does sound like motor height needs adjusted.
Paul

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Re: Another prop question

#6 Post by andymul87 » Tue Jul 17, 2018 11:26 am

Sounds like it's too high like others are saying. Also check to make sure RPM reading is accurate.
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wwind3
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Re: Another prop question

#7 Post by wwind3 » Tue Jul 17, 2018 4:46 pm

Tell me about the boat---is it rated for 90---or larger motor? Length, number of toons, weight, etc. If trimming up does nothing-you may be underpowered or too much weight in front of boat, etc..... FYI---I have 20ft Lowe 25in toons, 2 fishing seats up front-90 HP Merc Optimax, Merc SS prop 13 x 16in prop 27mph GPS
2009 LOWE SS204 25in logs
90 Merc Optimax
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bansil
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Re: Another prop question

#8 Post by bansil » Wed Jul 18, 2018 4:12 am

wwind3 wrote:
Tue Jul 17, 2018 4:46 pm
Tell me about the boat---is it rated for 90---or larger motor? Length, number of toons, weight, etc. If trimming up does nothing-you may be underpowered or too much weight in front of boat, etc..... FYI---I have 20ft Lowe 25in toons, 2 fishing seats up front-90 HP Merc Optimax, Merc SS prop 13 x 16in prop 27mph GPS
no idea on engine, it is original according to titles and paperwork I have
1990 Suzuki DT90

24 ft, 2 pedestal seats up front, no furniture (we use folding camp chairs) normal fuel load is about 15 gallons, 2 batteries, composite deck floor (about 250# more than marine ply and carpet) that about it
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Re: Another prop question

#9 Post by wwind3 » Wed Jul 18, 2018 8:17 am

What HP is it rated for ? Being a 24 ft boat is most of your problem. That's why trimming the motor has no effect-or very little. My boat sits with rear down so it tends to try to get on plane better...as you can see I'm still throwing a LOT of water at 27mph--but trimming does increase speed a lot....I can trim my motor up a lot before it blows out....I cruise at 18-19 mph at 4000-4200 rpms. Redline on my motor is 5850 rpms
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Re: Another prop question

#10 Post by curtiscapk » Wed Jul 18, 2018 8:51 am

Looks really high... maybe you should notch it like mine...
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Re: Another prop question

#11 Post by bansil » Wed Jul 18, 2018 3:48 pm

Been reading today and are pontoon boats that much different than flat and v boats?

Everything points to make sure the ventilation plate is barely skimming surface, if that is true i would have to raise my engine? (From memory), the area above vent plate is more rounded thus if it is under water it is drag and splash back.....i hate when the rabbit hole splits off.... :donno



Hopefully this weekend i can get pictures while wifey drives, still need to check prop also

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bansil
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Re: Another prop question

#12 Post by bansil » Sun Jul 29, 2018 9:19 am

Okay checked prop, it is aluminum 3 blade, 13.25 x 17

So is the aluminum 4 blade 13.875 x 11 the right choice? seems to be big difference between pitch altho I would have an extra blade....

No wonder there are 1 gazillion threads on props across the interwebz :mrgreen:

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Re: Another prop question

#13 Post by wwind3 » Sun Jul 29, 2018 11:04 am

bansil wrote:
Wed Jul 18, 2018 3:48 pm
Been reading today and are pontoon boats that much different than flat and v boats?

Everything points to make sure the ventilation plate is barely skimming surface, if that is true i would have to raise my engine? (From memory), the area above vent plate is more rounded thus if it is under water it is drag and splash back.....i hate when the rabbit hole splits off.... :donno



Hopefully this weekend i can get pictures while wifey drives, still need to check prop also
Yep--raise engine so that plate is even with bottom of mounting pod---which may be hard to do with your transom.. Your boat is too long to trim up enough to get your toons out of the water,,, would take a bunch more horsepower. Show us pics with your new setup.. Good luck.

I had mine out today--26 mph at 5800 assuming tach is correct. Cruising at 18 mph and 4000 rpms....
2009 LOWE SS204 25in logs
90 Merc Optimax
Motorguide W55 Wireless
Underskinning
28 GPS

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wwind3
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Re: Another prop question

#14 Post by wwind3 » Sun Jul 29, 2018 11:05 am

bansil wrote:
Wed Jul 18, 2018 3:48 pm
Been reading today and are pontoon boats that much different than flat and v boats?

Everything points to make sure the ventilation plate is barely skimming surface, if that is true i would have to raise my engine? (From memory), the area above vent plate is more rounded thus if it is under water it is drag and splash back.....i hate when the rabbit hole splits off.... :donno



Hopefully this weekend i can get pictures while wifey drives, still need to check prop also

Yep--raise engine so that plate is even with bottom of mounting pod---which may be hard to do with your transom.. Your boat is too long to trim up enough to get your toons out of the water,,, would take a bunch more horsepower. Show us pics with your new setup.. Good luck.

I had mine out today--26 mph at 5800 assuming tach is correct. Cruising at 18 mph and 4000 rpms....
2009 LOWE SS204 25in logs
90 Merc Optimax
Motorguide W55 Wireless
Underskinning
28 GPS

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bansil
Posts: 339
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Location: Watâ'gi lake...Beautiful Waters

Re: Another prop question

#15 Post by bansil » Tue Jul 31, 2018 1:40 am

How do i know if i need a hub kit :donno

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