PHP Warning: Use of undefined constant VBA_SCRIPT - assumed 'VBA_SCRIPT' (this will throw an Error in a future version of PHP) in ..../includes/functions_navigation.php(802) : eval()'d code on line 1 Faster Prop??
I am looking at buying a spare prop for my tinnie.
Its a 4.15 SeaJay SP with a 30 yamaha.
The main reason for the spare prop is for safety reasons as i have been in a boat that lost a prop and it wasn't much fun.
I figure if i'm buying another prop i might as well get something a bit faster for those dead calm days, to help bring the eastern bay a bit closer.
The current prop is a 12F x 9 3/8 from memory. (I figure that 12 is the pitch and 9 3/8 is the shaft size??)
Has anyone experimented with slightly faster props on a 30? I realise that faster top speed is going to come at the expense of torque and it will probably take a bit longer to get out of the hole but at the moment the top speed is a bit slow for the trip to moreton.
At the moment i get to top speed in no time flat and i think that the next pitch faster will be OK but i dont know if i'm gonna get into problems with cavitation etc.??
Hi Plaz, there are caveats everywhere if you would like a prop that looks after the engine for certain, but if you would just like to go faster look for a prop with less diameter and more pitch I do not know what is available for your engine but something with 9 inch diameter and 14P.
You could try leaving the diameter the same a 9 3/8 and just changing pitch to 14 but this depending where you are right now may not be verynice to the engine. The faster you go the more the hull lifts and the easier it is for the engine to push it so it may work (probably not from a 'correct' standpoint though) but without RPM/GPS numbers it's always guesswork.
I would try the first suggestion as it is closer to the same amount of 'work' for the engine but will find a faster top speed, lower speeds will be less efficient due to the decreased diameter - thats the trade off.
That makes sense mate. Obviously dont want to stress the poor 30 too much.
Most of the motoring i do is up on the plane and then flat out to where i need to go. If i do a creek fish or somewhere i need to go slow i'll throw the slower prop on.
I would like to see what the top speed and RPM's she does at the moment, a mate has a timing light that tells you the RPM, just need to get my hands on a GPS that tells speed.
Yeah Plaz if you get good rpm and speed numbers an informed choice is much easier, the caveat just means there are warnings in almost every direction with proping to get something you want can often mean taking something away you need
Do you think that going from a 12 pitch to a 14 and reducing the diam. down to 9inch will sacrifice too much bottom end.
I usually only fish with 2 in the boat and at the moment it gets me up on the plane quite quickly. Not really too worried if this is the only sacrifice, as far as i understand this will be my main issue.
Do you think a set of foils (or whatever they are called) will help in this instance to help get her up quicker, once the faster prop is fitted. I haven't bothered to look into them at the moment cause i've had no issues with its ability to get up onto the plane so far. Well there was once when we had it full of camping gear and 3 guys, but that was to be expected.....
The reduction in diam+ more P will initiate the highest prop slip when the hull is heavy in the water so around cruise and below (or all of the time if you are heavily loaded).
If you fit the 9diam it will mean the prop will be less efficient than the one you have on ATM BUT because you are chasing a better top speed once the hull lifts as a result of traveling faster the slip will decrease correspondingly until you reach your new higher top speed.
You should not loose too much bottom end just need a little extra throttle to make up for the slip the lack of diameter might induce (relative to your current prop) - very much like the theory behind proping the smaller 4 strokes.
But without good numbers it remains a suck it to see senario, but if what you say is correct the reduced diameter and +P might not make that much of a difference slow at least till you put a 3rd person in for a trip then it may do nothing well. Weight means much when the prop is not well suited to the application.
A foil is not a good idea yet IMO, if there is a real problem as a result, try one then or go back to the prop that works well ATM.
Reply With Quote
