Suggested prop for twin I/O

[degree]

I've got a 27' cuddy with twin 7.4's. I currently have three-blade stainless props (Quicksiler Laser II's) labeled: FC Quicksilver 48 A41 21P.

The boat weighs ~6,000 wet (and I don't mean because it's in the water), and it seems a bit slow getting up on plane (10-15 seconds). Also, it appears to have a healthy top end--something I neither want nor need.

According to Mercruiser information, WOT for this combo is 4200-4600 and I'm running 4500.

If I go to a four-blade prop, will I see a better 'holeshot'? Also, if I go to the four-blade, will I need to change the pitch to see proper rpm's at WOT?

I anticipate a great deal of help....

 

[Bondo]

Re: Suggested prop for twin I/O

Ayuh,......

I donno whether you need to go to a 4 blade or not,.....
But,....
Dropping to 19"s or 20"s will help the hole shot,+ get your rpms up abit......

 

[steelespike]

Re: Suggested prop for twin I/O

I've got a 27' cuddy with twin 7.4's. I currently have three-blade stainless props (Quicksiler Laser II's) labeled: FC Quicksilver 48 A41 21P.

The boat weighs ~6,000 wet (and I don't mean because it's in the water), and it seems a bit slow getting up on plane (10-15 seconds). Also, it appears to have a healthy top end--something I neither want nor need.

According to Mercruiser information, WOT for this combo is 4200-4600 and I'm running 4500.

If I go to a four-blade prop, will I see a better 'holeshot'? Also, if I go to the four-blade, will I need to change the pitch to see proper rpm's at WOT?

I anticipate a great deal of help....

It appears your running 21 pitch and 4,500 wot.not much room for a prop change a 19 would give about 4,900 rpm.too much unless you keep it 4600 or less.Without wot speed its difficult to evaluate your setup.The 19 would surely improve your holeshot.
Is the bottom clean/props in good shape? motors sound and well tuned?
I saw a test with a 11,400lbs wet 32 ft Proline with twin 250 outboards 14.75 X 17 props. plane in 8 seconds.maxes at 45 mph.5,900 rpm.It seems even allowing for the huge weight of twin 7.4s in the stern you should match that.

 

[SuperNova]

Re: Suggested prop for twin I/O

A big part of the problem is there is an awful lot of weight in the stern (twin big-blocks) and not a lot of boat length to offset that weight. I have dealt with twins in short boats a few times now and it seems the best answer is to get trim tabs if you don't have them or start using them to help get on plane if you already have them. A lower pitch prop may help some, but it is sort of a bandage for the real problem. I am surprised it was even suggested by one of our "technical authorities" even though you stated you are already running close to your absolute max rpm as it is. I also don't feel that changing to a four-blade prop is going to make much difference in your case, either. It truly is a matter of too much weight at the stern--you probably get a lot of bow lift before you get on plane as well. Another thought is: Make sure your outdrives are trimming all the way down, too.
--
Stan

 

[degree]

Re: Suggested prop for twin I/O

A big part of the problem is there is an awful lot of weight in the stern (twin big-blocks) and not a lot of boat length to offset that weight. I have dealt with twins in short boats a few times now and it seems the best answer is to get trim tabs if you don't have them or start using them to help get on plane if you already have them. A lower pitch prop may help some, but it is sort of a bandage for the real problem. I am surprised it was even suggested by one of our "technical authorities" even though you stated you are already running close to your absolute max rpm as it is. I also don't feel that changing to a four-blade prop is going to make much difference in your case, either. It truly is a matter of too much weight at the stern--you probably get a lot of bow lift before you get on plane as well. Another thought is: Make sure your outdrives are trimming all the way down, too.
--
Stan

I have K-Planes on the boat now. Just so I understand this...

Dropping the tabs will give me stern lift and put me up on plane quicker, right?

I failed to mention that, yes, the drives are trimmed in all the way. There is bottom paint on the boat but the props and drives are clean and in good condition.

I have read that a four-blade will give you a better 'hole shot', so I was wondering if I kept the same pitch (21) with a four-blade, would that help? Or do I need to change the pitch when going to a four?

 

[steelespike]

Re: Suggested prop for twin I/O

Yes dropping the tabs will help hole shot.
The four blade is said to improve hole shot.Whether it will help your problem I can't say.The prop doctors will have to tell us if the pitch should remain the same.By the way the main request in props is for improved I/O hole shot.

 

[MikDee]

Re: Suggested prop for twin I/O

IMO, a 4 blade will usually help get the stern up, and give you better hole shot, but scrub a little speed, because there's more surface area with the extra blade, but it is harder to spin because of this also. Meaning you'd have to drop in pitch to maybe an 18" Stainless, or 19"Aluminum. This is just a general estimate, if you could borrow a couple props, or buy with an agreement to try them, and switch if need be, would be your best bet.

 

[TilliamWe]

Re: Suggested prop for twin I/O

Combine steelespike and Mikdee's answers and you have your best course of action. Borrow four blade props in the 18-20" pitch range and see if they help.
SuperNova is right about twin big blocks in the back of a 27' boat. That's a lot of extra weight back there. Make sure you don't have anything back there like 4 batteries, gear, a full water tank, etc. With "just" a cuddy, there isn't a lot of forward weight in your boat. It may never perform exactly like you want.

 

[degree]

Re: Suggested prop for twin I/O

Thanks, guys. You all have been a great help. I really don't care about the loss of some top end, as I had said earlier, I don't need it. I know there is alot of weight on the stern, and with a cuddy (as you mentioned) there isn't much to help hold the bow down--which is why I feel like I'm on a spaceship when I give it throttle (it wants to go up--up--up).

I'll try a different pitch and will be going to aluminum as I understand they are a bit more 'forgiving' when encountering something solid !!

 

[Bry21317]

Re: Suggested prop for twin I/O

So did you ever try the Trim tabs to see if they helped? I was just wondering as you never answered that part of the question.

I am guessing that you did, but never saw you state it.

Bryan

 

[degree]

Re: Suggested prop for twin I/O

I didn't try the tabs as they weren't working (solenoids were bad), but will do so next season.

 

[SuperNova]

Re: Suggested prop for twin I/O

I have K-Planes on the boat now. Just so I understand this...

Dropping the tabs will give me stern lift and put me up on plane quicker, right?

I failed to mention that, yes, the drives are trimmed in all the way. There is bottom paint on the boat but the props and drives are clean and in good condition.

I have read that a four-blade will give you a better 'hole shot', so I was wondering if I kept the same pitch (21) with a four-blade, would that help? Or do I need to change the pitch when going to a four?

1- yes, the tabs turn all that bow lift into more stern lift and less bow lift and will help a difficult-to-plane boat plane off easier.

2- If you switch to a four blade (and I have done this experiment) it will help you slightly, but not enough to justify the added expense. With twin outdrives you are already getting a lot of bite in the water, you shouldn't really need more, unless your current props are really dinged-up.

3-If you go to aluminum props you may make your problem worse; aluminum blades tend to flex more under load and will reduce your boats ability to get on plane slightly.
--
Stan