James c harrell

My Feedback: (18)

Can someone tell me the difference between surface and submerged props? I looked at the prop chart (Octura) and under the suggested prop size part it advises the same prop for both sumeerged and surface applications. Maybe the size changes but are the props shaped different or something?

Deathwish

My Feedback: (6)

submerged is under the water (like a jet drive) surface is right at the surface (used on most speed boat's)

jordan gutteridge

hello james the actual shape of the two props is different some one correct me if im wrong but im sure the submerged drive props are alot more rounded meaning they are not as aggresive because it doesnt need to be when all blades of the prop are submerged. whereas a surface drive prop is more pointed and more aggresive because the prop is only supposed to be half in the water. suface drives are most common especially on gas boats like monohulls, cats, riggers etc the only type that i know of that do require a submerged drive is a fsrv which is very flat bottomed. if you are undecided which prop to get  send me a pic or descride the hull and i will be able to advise you

hope this helps 
regards jordan 

James c harrell

My Feedback: (18)

I had thought the props were different as well but got a little confused when I looked at this chart. http://www.funrcboats.com/prop_chart1.htm Notice at ther top a couple props appear for both surface and submerged. I changed the motor in one of my boats and looked on there for a starting point on the prop size. The boat I am working with is this one. It now has a K&B 6.5 and a pipe.

James c harrell

My Feedback: (18)

Just a note. I have changed the solid shaft out for a flex drive. I found a couple of better pics.

*delete M i k e u p delete*

I hope you changed cable to next size up from .130. Submergred can strain cable pretty good. Don't forget heat shrink to keep water out but make the angle where u-joint was alittle smoother with liner. Hint; sand cable some some where bend is great to cut friction.

James c harrell

My Feedback: (18)

I did go with the .250 flex stepped down to a 3/16 prop shaft. Put a new teflon lined tube on it. The shaft spins real smooth and free. I put a 1445 prop on it but still don't understand how to tell if a prop is a submerged or surface. I know if a boat needs a surface or submerged but which props are which? The 1445 prop seems by the prop guide to have the same dimensions as the X445 that it recommends for a 7.5 deep-vee submerged and I had one so I will try that one for now. I guess I will have to experiment to find the right one after I break the engine in a little.

engineman351

James, From the dialog I assume you are running a 7.5cc engine.

DEEPVEE - INBOARD - SUBMERGED PROP 7.5 cc - X445, X447, X645, X646
DEEPVEE - INBOARD - SURFACE PROP 7.5 cc - X450/3, X452/3 X455, X457, X646/3

If you look at the Octura chart you will see that the SURFACE drive props are a little bit larger. The /3 blade props also load the engine more so 3 blade props act like larger 2 blade props. Surface drive props are usually larger because one blade is in the water doing the work. Looking at the pic's, your hull is definitely a SUBSURFACE or SUBMERGED drive...so you need to use the smaller diameter props since there are two blades in the water. Also, a SURFACE drive either has the stuffing tube running extremely close and parallel to the keel...or in most modern application the entire stuffing tube is inside the hull with the propshaft exiting the transom at the very bottom of the vee so only half the prop can hit the water.

engineman351

James, I just went back thru the posts and I see you said the boat has a 6.5 K&B (not a 7.5)...I would definely try the X445 and X447 props on your setup. Make sure they are sharpend & balanced. RC

James c harrell

My Feedback: (18)

When my friend gave me these boats he also gave me a bag of parts. Among them were some props, mostly bigger for my .81 tunnel hull but there were a couple smaller 1445 props that, by the chart are the same as the X445. The shape of them is a little more rounded but the picth and size are the same. Hence my question on the submerged and surface issue. All is on hold now as I have found a bearing in the 6.5 that is pitted,many years of storage, and I won't run it untill I have new ones. Everthing else in the motor is brand new. I looked up the two props and if I can find the pics of them I will post a pic to show the difference.

James c harrell

My Feedback: (18)

found the pics I was talking about. If the pitch and diameter is the same should it be close? The left is the 1445 and the right a X445.

engineman351

James, If you checked the Octura charts I am sure you found that both these props have the same diameter and pitch (1.77/2.48 in). The difference is the shape. The 1445 is in the series of props that provide 'lift'. Lifting props are mostly used on Hydros. The 'X' series of props are more 'cleaver like' in shape and do not provide as much lift as the non=X series props. The 'X' series is usually suited better for a Dee-Vee that needs the transom to settle into the water for good handling. On your DV I'd try using the X445 first. BTW...if you need a bearing for the 6.5 you can check the K&B site for availability, but it might be better to remove it and measure, then see if you can order one from someplace like Boca Bearings.

James c harrell

My Feedback: (18)

Problem being I don't have a X445 but have two 1445's. I had to measure the bearing. Mecoa doesn't list the right size and I can't get an answer on the tech forum.I called Boca and the tech there was great. He hooked me up with the best ,not ceramic but more than enough for what I want. For 12 bucks a piece. I will get them in and look for a prop after. The boat I am running is old and quite heavy so maybe a little lift would be good??? At least I can get an idea of if the pitch and size is right befor I get a good X prop. Money is scarce here.