Trying to find correct prop

[tbalt]

Hi,<br />I have a 2004 25' Odessey tritoon with a 2004 Honda bf200 4 stroke. My recommended wot is suppose to be between 5000 and 6000 rpm's. I've tried three props, The original was a stainless Honda logo 15.25" dia 19 pitch with a wot of 4700 rpm's and 42 mph on GPS. The next prop was a stainless Solo 15.25 dia 17 pitch giving me a wot of 5800 and 33 mph. And finally Michigan Vortex aluminum 14.5 dia 19 pitch which gave me a wot of 5600 - 5700 rpm's and speed of 35 mph. All three props gave me good bow lift ( the two stainless were better for lift ), but the solo and vortek gave me alot more ventilation during trim and while slight turning trimmed. I know to lower trim during hard turns. The motors cavitation plate is level with the bottom of the toon but there is a 3/4" keel that extends below. The motor can't be lowered do to transom design.<br />My question is what prop do you guys recommend ( brand, # of blades and size )?<br />Also what would it hurt to run a rpm lower than recommende if it yeilds higher speeds? And would a hydrofoil help the ventilation problem?<br />Thanks Tom

 

[ThomWV]

Re: Trying to find correct prop

I wouldn't use any of them.<br /><br />The closest one you have there, assuming that you had good speed numbers for the original prop, is the Solo and it might be OK if someone would bend a little more cup into it, but as it is it appears that you have an awful lot of slip. I don't know the lower unit reduction on a honda engine (probably around 1.8:1) but you need to find out what it is (should be in your owner's manual or in sales literature) so you can do a quick calculation on slip. Find one that will get that slip down to about 10% or less and you should do a lot better than what you are seeing now.<br /><br />Thom

 

[rickdb1boat]

Re: Trying to find correct prop

If I had to use one of them. I would use the Honda prop and have it re-pitched to 18". That would allow your RPM's to come up to 4900-5000 and keep you in the best speed range you have found so far and probably with a better hole shot. Might even try a Honda 17" pitch and see what happens. Are you friendly with your dealer? He may work with you on this...

 

[tbalt]

Re: Trying to find correct prop

The lower unit ratio is 1.86:1<br />How do you calculate the slip to figure out the correct one to use?<br /><br />My dealer is a little hard to deal with, they traded the Honda prop for the Solo but said they didn't want to keep opening all of there prop boxes.

 

[ThomWV]

Re: Trying to find correct prop

Tbalt,<br /><br />With a 17" pitch prop with no slip you will move at 8.65 MPH per 1,000 RPM. So at 5,800 RPM with that prop the fastest you could possibly have gone with no slip would be 50.2 MPH but you were only going 33 MPH. So, divide 33 by 50.2 and you come up with .657, or 65.7% efficiency. That means your prop has 34% slip at WOT. That is not very good. However the prop is operating up at the top of the RPM range so maybe if you had some cup bent into it that would come down at the same time it improved the slip (cupping will normally help reduce slip).<br /><br />When you were running that 19" prop your theoretical speed per 1,000 RPM would have been 9.67 MPH. When it was turning 4,700 RPM if there had been no slip it would have had you going 45.5 MPH so your 42 MPH means that it was running at about 92% efficiency, meaning it would have been a great prop if it had a little less pitch. The problem is that if a prop shop goes to take pitch OUT of a prop you might as well take the thing and toss it in the trash right now and save yourself some money.<br /><br />What would look to be a real winning ticket for you, that would cost you an arm and a leg, would be a nice stainless one in a 4-blade with a modest cup in it, and maybe ventilated too just for the hole shot. If you found something like that in about 18" I think you'd be in hog heaven. I'd guess a top end somewhere in the mid to high 40's and a hole shot that would please you greatly. The very worst thing that could happen if you got a prop like that was it was reving a bit higher than you liked and you could always have a prop shop bend a little more cup into it - which would further improve your hole shot and just cost you a little bit of an already ample top end anyway.<br /><br />That's how I'd look at it.<br /><br />Thom

 

[tbalt]

Re: Trying to find correct prop

Thom,<br /><br />That was some great info, Michigan Wheel makes a 14.5" x 18" pitch stainless prop for my motor. Is that a good choice for a four blade or is there another brand better? Also would that help with some of the ventilation?<br /> <br />Thanks Tom

 

[tbalt]

Re: Trying to find correct prop

Thom,<br /><br />I got the prop brand wrong it's a Quicksilver 4 blade 14.5" x 18" not a Michigan Wheel.

 

[ThomWV]

Re: Trying to find correct prop

As for the calculations, that is just a function of gear ratio and prop pitch so it really doesn't matter much what the brand is. I am not familiar with the Quicksilver, other than to know the name, so I can't comment on if it is the right choice for you or not.<br /><br />The thing about the 4-blades is that they work very well with heavy boats and the additional surface area of the 4th blade really lets them hook up. It also allows the engine to be run a bit higher which of course reduces drag in the water which is always to your advantage.<br /><br />At any rate, and I don't do this to promote another message board, but there is a fellow named "Dunk" who can be found on the Florida Sportsman message board, as well as at the WMI Saltwater fishing and the Hull Truth message boards on most any day. Dunk is a Marine Surveyor but more importantly he is very well informed as to props and which makes and models are best suited to which purposes. You might want to post a question to him on one of those boards. He will give you more reliable advice than I could, he's a lot better informed on this subject than I am. I could probably point you in the right general direction but he could give you specifics.<br /><br />Thom

 

[tbalt]

Re: Trying to find correct prop

Posted Dunk but have not seen a reply, anyway I talked the dealer into trying more props. Were going to stick a Solas 3 blade HR Titan 18" pitch on this weekend. Hope this is the answer.<br />Tom

 

[tbalt]

Re: Trying to find correct prop

Thom,<br /><br />Prop update, My dealer gave me a new Honda logo ( Powertech Brand ) 3 blade 15.25" x 18" pitch this week. The prop has a high aft rake and extra cup. My boat now achieves 46 mph @ 5500 rpm's full of gear, family and full tank of gas.<br />Looks like you figured the pitch size right!<br />How many mph per every 1000 rpm's should this 18 pitch prop produce. <br /><br />Thanks Tom