new prop for tldi 115

[rubadub]

Hi guys,

i own a deep-V 5m RIB with a toha tldi 115. With normal weights (i.e. 120 lit of fuel, 50 lt. water tank, all the extras plus 2 persons) it max. @5.800 rpm and 37 knots, with a 13,25X17 3-blade prop.
i need a 2nd prop anyway (safety reasons) and was thinking of a 4 blade aluminium one, again 13,25X17. Any opinions on that?

I know that if one goes from a 3 blade to a 4 blade, then the diameter must go down by one (i.e. 12,75 instead of 13,25) , as to maintain the same max rpm's, but i'm thinking that a 13,25 will push the boat much better than the 12,75 one, and even if the max rpm's drop by 200-300 (as expected) i will still stay within the range given by toha (5.150-5850.)


Thanks in advance

 

[Silvertip]

Re: new prop for tldi 115

You are mistaken. Prop diameter does not "have to go down" just because you change pitch or number of blades. The reason you see prop diameter changed is because of the design of the prop. People worry way too much about diameter when they should be worrying about setup before thinking about props. So the first question is why do you feel you need a four blade prop? It probably won't go faster, will probably pull the engine off its recommended WOT rpm, will probably use more fuel because the throttle has to be open further to maintain the same speed because of lugging, but may help hole shot and decrease top end. So why would you want to decrease engine rpm which means the engine is lugging. Yes, you are still in the power band but why not prop for the top end of the band which is where it should be. Lastly, props are designed for a specific series of engines so 13-1/4 inch props are typically designed for mid range engines like yours. Now within the designs for your type of engine, each manufacturer will have a range of pitches (13 - 25 for example). If you checked each of the props in that range all of which are the same design, you will find that the lower pitch props are slightly larger in diameter than the high pitch props. It all has to do with design. Select a prop designed for your engine, select the pitch and diameter takes care of itself. In your case, do not use diameter as the first criterea. Look for a prop model designed for your engine -- that means one that physically fits the engine and is designed for it. Every prop manufacturer also has at least two or three propeller models or series so you need to consider that as well. Just because a prop from vendor A and B both have the same pitch does not mean they perform the same. Then select the number of blades and pitch you need. Diameter will take care of itself as indicated earlier.

 

[steelespike]

Re: new prop for tldi 115

Prop diameter is a product of the prop design.You normally don't even consider diameter except in certain very specific applications.
The 4 blade for your application will be whatever diameter.As you may know
the 4 blade will generally help low end performance at a slight sacrifice of top end.If I was doing it I would consider the Turning Point Rascal and Hustler props in 17" pitch. SS performance at AL prices.All the tests I've read indicate they give an overall performance improvement.

 

[rubadub]

Re: new prop for tldi 115

With the 4blade prop i will loose in the top end, but will gain speed in the mid-range (4,000 rpm's, i.e cruising rpm's). I'm thinking about a 4 blade one as i need a second prop for backup, and there is no point going for a 3blade one as i 'm pretty satisfied with the one i have now, so why not go for one i can use in diffenert situations?Moreover, it will lift the stern and will increase the handling in bad weather.
thanks for the info steelespike, will have a look and come back if i have more q's.

Thanks m8

 

[boat1010]

Re: new prop for tldi 115

I tried running a 4 blade with the same diam. and same pitch on my boat. No JOY!! my 454 wouldn't push it nearly as well as the 3 blade. I could tell it was smother and handled a little better. But like ya said, no sence having two props the same. Just depende what you are looking for. Top end low end or the crusing speed. Best thing is to try to find a friend that has one you are thinking about buying. that way you know for sure.. Only takes a few min to change the prop and try it out.

 

[rubadub]

Re: new prop for tldi 115

another thought is to go for a 3blade 13,25X19, and see if i hit the jackpot, gaining in speed and hopefully not loosing too much on planning times or lowering the max. rpm's... any thoughts?...

thanks again guys

 

[steelespike]

Re: new prop for tldi 115

Don't like the Turning Point? No prop is a garantee but I've seen tests going from stock AL props to the Turning Point generally improvment across the board. About $90 for the prop and$47 for the hub.

 

[rubadub]

Re: new prop for tldi 115

i've heard good things about turning point, only problem i am in Greece, and if unlucky the customs can take ages.....

 

[steelespike]

Re: new prop for tldi 115

Ouch!
Maybe a dealer could order one with less hassle?Or perhaps someone handles them.If you can find a good prop shop you could have the 17 reworked to an 18 or have a little cup added.Just be sure they know what they are doing.I guess you would still be a prop short.I guess you could do the 19 and have it reworked to a 18 if its too much.Going with a 19 could knock off about 400 rpm.I feel the DFI 2 stroke can handle it easier than a typical 4 stroke but I don't know how well your style boat gets up on the water.