Props and Chine Walking (My Specific Case)

[Pennstater]

I have an OSE CNC Machined Prop, number 4814. I know the diameter is 48mm, and I calculated the pitch ratio as 1.4 based on the total pitch value (2.65” ~ 67.2mm) provided on OSE (which jives with the model number 48=diameter; 14=pitch ratio (1.4)). I am thinking this would be the equivalent of an Octura x448; is this correct?

Would this prop be considered a high-lift or low-lift prop (Octura bills it as a “general purpose” prop suitable for mono’s and cat’s (maybe other types))?

Here is the reason I ask…

I have a 40” Deep Vee that I converted from glow to FE. I am running a Leopard 4092 930Kv on 10s (2x5s in series - high-voltage, low amp). Prop calculators suggested a 48mm prop, so that’s where I started (using the CNC version so I don’t have to sharpen/balance the prop myself). Note that the stuffing tube exits the bottom of the hull and extends back to an Octura strudder. The strut positions the stuffing tube about ¾” from the bottom of the “vee” (see crude diagram). I do not have trim tabs or a turn fin installed (the boat turns fine; I don’t see any leaning towards one side, etc.). Also note that after about eight minutes of running the boat around half throttle and lower, none of the components are remotely warm and remaining battery capacity is around 35% to 50% (voltage per cell is around 3.75v).

_______hull_________|--------|
........\_________________|_/ |
.......................................\ |

I can only run the boat at about half throttle – anything more and it starts to chine walk (half throttle is faster as an FE as it was at full throttle on glow (.60)!!!). When I see it go by at this [elevated] speed, it looks like the boat is riding on the prop only, with little to no part of the “vee” in the water. A little slower, and the boat rides like a dream.

I can only mount the batteries to the outside of the hull, as the hull has 5” rails epoxied in place, so moving to the lowest part of the “vee” is out. The batteries are positioned to provide a COG around 30% (measured from the transom). I haven’t fooled around with moving them forward or back as of yet, thinking that maybe a different prop might help.

Question is, which way do I go in prop size? Should I go to a smaller diameter, higher pitch prop (x645), a larger diameter, same pitch prop (x450), or to an “m” prop (whatever those are)? Or do I just buy several sizes/pitches around my current 48mm and just experiment (the props are $20 each, so I’d like to try and make educated guesses here). And what about the whole high-lift vs. low-lift prop – I would think I would want a low lift prop – what are specific low-lift props?

(This last question is a bit off topic from "Prop Talk" but please bear with me)...

Or, should I keep the same prop and try moving the COG back? As it is right now, I think trim tabs might be useless at this speed (with no other changes) as it seems there is little to no hull in the water.

Thanks,

Matt

[T.S.Davis]

Your diagram makes it look like the stuffing tube comes out the bottom and that the strut is below the keel 3/4" If that's accurate the prop has little to do with the chine walk you're experiencing. Well some but.....

The prop you are using and the most common props we use for that matter are surface piercing props. The center of the hub is expected to be just above the actual planning surface of the boat. So that only one blade is in the water at a time. So it needs to be behind the boat and approximately level with the keel.

If your prop is below it will try to get itself to that surface. With 10s in a 40" boat you have enough power to lift the whole boat out of the water so that the only thing you're riding on is the thrust cone itself. If none of your boat is riding in the water it's going to bounce from edge to edge like crazy.

[photohoward1]

How about an actual photo of the set-up.

[Pennstater]

I'll try and get a pic uploaded tonight. I'm at work and have been putting off asking this question for the last week but it's really got me scratching my head, so I took some time at lunch to post the question.

The stuffing tube does exit through the bottom of the hull and is roughly 3/4" below the keel. This is an old glow boat from about 25+ years ago (I don't recall surface drives (Stingers) then).

[T.S.Davis]

It may have worked on that power back in the day. The power your putting down is likely in the 4 to 5 horse power range. That's if you keep the amps low like you suggested. You could likely push that motor out to the 7.5 horse range without taxing it too hard.

You'll be hard pressed to find a sub surface prop that isn't design for a tug boat.

If you decide to change it we'll walk you through how to do it.

[Pennstater]

Thanks for the quick replies - much appreciated.

When you say "If you decide to change it we'll walk you through how to do it" are you referring to moving the stuffing tube such that it exits at the very bottom of the "vee" and using something like a Stinger. Or perhaps re-bending the stuffing tube such that it essentially eliminates the 3/4" gap between itself and the keel (and adjusting the strut up within the strudder assembly)?

I like this hull as it has some sentimental value to me, but perhaps I am simply putting too much power into it. I'm not sure moving the stuffing tube around will be an easy task, so if that is the suggested course of action, I may leave it like it is and just be happy with half throttle runs. Perhaps I'll move that power system into another boat and start off with something a little more modern (I do want a larger boat)???

Regardless, I'll post a pic or two tonight so you can see it properly. Thanks again for your replies.

[T.S.Davis]

To get it to run right you'll want to have the stuffing tube exit the transome just above the bottom of the vee. You don't necessarily have to go to a stinger to do it though. Pics will help us give you some guidance.

[photohoward1]

If you do like it for the nostalgia run it on 5 or6s. Like terry said not hard to rework it.


Sent from my iPhone using Tapatalk

[Pennstater]

Here are a couple of photos of the stuffing tube and strudder at the transom...

IMG_20160302_191038.jpgIMG_20160302_190953.jpg

[dasboata]

you need to go surface drive with that Dumas lets see some pics of the inside ! ,, the strakes running all the way to the back adds to the lifting the hull also !

[Pennstater]

It's an old Wardcraft. My dad found the "manual" in his attic - just a big tri-fold. Judging by the way the people were dressed in the pictures, it looks like mid-to-late 70's!!!

I'll try and get some pics of the inside uploaded by tomorrow.

[T.S.Davis]

Unless the innards are a disaster it shouldn't be that bad raising that hardware up the transom.

[Pennstater]

@T.S.Davis - that's funny - "Unless the innards are a disaster". I'll get some pics up tonight, but imagine a very old boat with a lot of epoxy in places (no CF in here). The biggest thing in the way is the "radio box" - a simple wooden box with an acrylic cover. I have no problem ripping this out (if needed) and replacing with something else later. My concern will be removing the existing stuffing tube without doing collateral damage.

You mentioned "no need for Stinger" - do you think the existing strudder can be retained and the strut just gets moved up higher in the strudder bracket (assuming the slot in the strut is long enough)? You can see in the pics above the prop is not set that far behind the transom. In a surface setup, would this close proximity [of the prop] to the transom be problematic? Or do I go with a different strut/rudder assembly? I would love not to have drill a bunch of new holes in the transom (I just filled a bunch of them before re-painting when I started this project).

Should this thread be moved (if "yes", I don't see how to do it myself)?

Thanks all!!!

[T.S.Davis]

Well, depends on how much performance you really want from it. A stinger would be better IMO. Gets the prop out from the transom a bit.

If you're just wanting to have fun with an old boat that means something to you then I would consider just moving the strut up. You could move the whole bracket straight up. Filling the old holes is easy. If you just slide the strut up into the bracket without moving the bracket you'll likely whack the bracket with the prop. There are guys that totally believe in the short strut but it isn't optimal. You could make a bracket that looks just like the one you have but extends your strut and rudder back further. If you follow what I'm saying. Then replace the shaft and get a new push rod for the rudder and you're in.

Think about what you want to do and we'll git ya through it.

[srislash]

@T.S.Davis - that's funny - "Unless the innards are a disaster". I'll get some pics up tonight, but imagine a very old boat with a lot of epoxy in places (no CF in here). The biggest thing in the way is the "radio box" - a simple wooden box with an acrylic cover. I have no problem ripping this out (if needed) and replacing with something else later. My concern will be removing the existing stuffing tube without doing collateral damage.

!

I recently did this to a big ole 45" Dumas hull. Too much epoxy to hold a stuffing tube. Also under Rx box. Box was easy to move and the epoxy I got out using a Dremal MultiMax. You know the ones with the oscillating flat blade. Use the metal blade on it and don't be afraid to bend the blade for easier angles. Rent one if you don't already have one
But if you buy one you may be surprised how many jams it helps you out of around the home.