RPM's at WOT vs RPM's @ Hole shot

[Augoose]

I've got a VP 5.0 GL carb'd V8 with a 17p 4 blade aluminum prop. I rebuilt the carb last year and overall the boat runs and idles very well. My question is in regards to tuning and proper propeller.

At WOT my boat runs exactly where it should be according to VP which is at around 4600 rpms. During a hole shot with a full tank of gas, two adults (me driving and wife in passenger seat) and one 60 lbs kid in the bow, my boat is at 3000 rpms until the boat planes. After it planes the rpms increase up to the WOT range as mentioned. The problem is that its pretty slow getting up on plane.

I'm wondering if the 3000 rpms at the hole shot is adequate?

 

[82rude]

yes.short answer your not going to get high rpm at holeshot as the motor and prop have to build up to it.have you considered maybe trim tabs to help you ?

 

[Augoose]

I honestly have never thought about trim tabs for my boat as I just didn't think it was "large" enough to need trim tabs - but you're right, it would likely help.
Thanks for letting me know that 3000 rpms at the hole shot is not abnormal- at least I can rule out tuning/prop.

 

[Augoose]

I honestly have never thought about trim tabs for my boat as I just didn't think it was "large" enough to need trim tabs - but you're right, it would likely help.
Thanks for letting me know that 3000 rpms at the hole shot is not abnormal- at least I can rule out tuning/prop.

 

[Starcraft5834]

You have the 4 blade which is best to assist quickest plane..tabs worth considering..with those you will likely achieve plane at lower rpm

 

[steelespike]

What is your hole shot in seconds/minutes?Do your trim down for hole shot? What is the wot rpm and GPS speed?

 

[Texasmark]

What kind of hull shape do you have? A deep V with significant dead rise at the transom takes longer to get out than a flat bottom of sorts. Part of the price you pay for the soft ride.......but I for one will take the soft ride. Grin. Rpms are part of the horsepower equation. 3000 in the hole is/should be well above the torque peak and you should be getting good HP delivery at that rpm. So when you reply to Steelspike's questions, how about adding this answer to it.

Mark

 

[Robbabob]

Adding to input, consider where you boat.... the aluminum is more forgiving when you hit something, but it's also more flexible and not as efficient as SS. Hole shot will be better with a SS prop. It will also cause more damage if you have a fear of hitting submersibles.

Good luck!

Edit: The prop cost is higher with SS. The damage it "might" cause is in the out-drive.

 

[Augoose]

No Title

What is your hole shot in seconds/minutes?Do your trim down for hole shot? What is the wot rpm and GPS speed?

Steelspike, I haven't timed it exactly, but its a good 2-3 seconds longer than a 2001 19' Stingray with the 4.3 merc that I've had access to for years. I suppose in my mind I keep expecting my boat to get up and go as quickly as that boat which I know is MUCH lighter- maybe might expectations are too high. Next weekend I'll be on the water again and I'll record the time it takes to get to plane under different loads. As for trim, yup - we are trimmed all the way down to start with. WOT rpm is about 4600 and at around 48/50 mph. My lake is seldom smooth enough to really go flat out but I would estimate that its around 48 mph or so.

What kind of hull shape do you have? A deep V with significant dead rise at the transom takes longer to get out than a flat bottom of sorts. Part of the price you pay for the soft ride.......but I for one will take the soft ride. Grin. Rpms are part of the horsepower equation. 3000 in the hole is/should be well above the torque peak and you should be getting good HP delivery at that rpm. So when you reply to Steelspike's questions, how about adding this answer to it....Mark

Texasmark. I'm not sure how to describe the hull shape but I believe that it would be classified as a Deep V - here is a photo from the internet - not my personal boat but its the same model. Based on what you say however I can relate to the ride quality - my boat rides far better than the Stingray with the better hole shot both in handling wake and rough water but also in a softer ride in general.

Thanks to everyone for their replies. My main concern was to compare the hole shot rpms with WOT rpms. It makes sense that the boat is still increasing torque during the hole shot and it sounds like 3,000 rpms is normal and expected.

 

[steelespike]

When comparing hole shot of I/Os there is a lot of weight back there and the 5.0 is surely at least 100 lbs more than a 4.3
I think if you took a 100 lb person at put them right at the stern it would affect hole shot.
When comparing different years there are 4.3s with significantly more hp than a 5.0 220 to 200. I think your boats are in roughly the same years so hp are probably a more typical comparison. If the Sting Ray had a harder ride it probabley had a flatter bottom and would be quicker out of the hole

 

[MikDee]

Finally a picture of your boat. It looks like your boat is a bit of a back heavy "pocket rocket". I had a boat one time like that as well, I'd say you need a Doel fin to help with hole shot. You could get Smart tabs instead for a few more bucks, and more labor to install, but you could experiment with the Doel fin, and I think in the end, you'll be happy with it.

 

[kjsAZ]

If you want to experiment with an original Doel-fin you can have mine for the price of shipping (used for maybe 10h total). My boat came with it installed by PO and ran like a drunken sailor and had problems to stay on plane at lower speeds. Since it's removed it runs like it should. Much faster on plane, stays on plane at lower speed/RPM's and handles as it should. Results are different from hull to hull so it may work for you. Shoot me a PM if interested and I'll calculate what USPS or UPS or Fedex would charge.
It would also win me a bet with a friend (who gets rid of it first) who also wants to get rid of the one he removed for the better.....
To be honest, I would install Bennett SLT-10 (all stainless) or at about the same price Nauticus-SX in plastic...

 

[MikDee]

I've put bennet tabs on one of my boats, expensive, and slow reacting. Smart tabs are automatic, better, and cheaper.

 

[Tabman]

I've put bennet tabs on one of my boats, expensive, and slow reacting. Smart tabs are automatic, better, and cheaper.

MikDee,

The SLT-10 that kisAZ refers to are "automatic" type Trim Tabs.

 

[jestor68]

I'd never install trim tabs that I couldn't control. Do it right, or don't bother.

 

[bruceb58]

I had a Doel Fin on a 21' cuddy. I took it off because it would cause the stern to wash out in a tight turn...No thanks!

It also reduced my top speed. Not a fan.