Performance issue

jbied72178

Cadet
Joined
Aug 17, 2022
Messages
7
Anyone with a cabrio 274 that has a single 5.7 mercruiser 350 mag mpi. How long does it take you to get to plane? Mine takes about 30 ‐35 seconds with only 2 people on board which seems slow to me. Had 4 people onboard the other day and would not plane without sending people toward the bow in the cabin which I find hard to believe is normal. Boat is new to me. Been having issues all summer.
 

Scott Danforth

Grumpy old guy who plays with boats
Joined
Jul 23, 2011
Messages
41,999
welcome aboard

you could be over-proped, could be other factors

are you trimming all the way down (in) for the holeshot?

does your prop allow the boat to get all the way up to 5000 RPM?

have you moved the beer cooler to the bow?

have you tried with your trim tabs down slightly?
 

jbied72178

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Joined
Aug 17, 2022
Messages
7
-Prop is correct: 22p 4 blade
-Engine trimmed down fully
-Trim tabs up or down make little difference.
-Once on plane the rpm's and speed take off: can get 4600+ rpm and 35+ mph
-Not overly loaded boat. Little fresh water in the tank as we use city water hookup at dock. Waste water emptied regularly. And 1/2 tank gas.
- checked fuel pressure and is good: 43psi at WOT
- checked compression and its good: 148-154 at all cylinders
-fuel injectors cleaned and good
-new plugs, wires, cap, and rotor

I wasn't able to be at the survey/sea trial when we purchased the boat. My wife went to that but can't remember if the boat performed better or the same as it does now. So I'm not sure if there is an issue or "that's just the way the boat is".
 

QBhoy

Admiral
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Mar 10, 2016
Messages
6,995
Sounds like you are over propped as AD suggests. These mpi really need to be at or near the top of the rpm range.
That said, these kind of boats are greatly affected by design. As in, lots of weight towards the rear, if you have passengers and more crucially, lots of fuel onboard. The tank is fairly well aft. A full tank on boats like these is the equivalent of carrying a big 4 stroke jet ski on the back of the boat !
Finally. Just around the prop. I’d think it perhaps unusual for any prop to be “standard” on a boat usually. Especially a 4 blade. Is it a bravo 1 presumably with you saying just the one prop ?
 

jbied72178

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Aug 17, 2022
Messages
7
It is a Bravo 3 so dual prop. I believe it originally had 3 blade props and previous owner upgraded to the 4 blade. I will double check but I was told that the 22 pitch was correct for the boat. I don't believe we a carrying too much weight. Only 1/2 tank of gas, very little fresh water, and mostly empty waste tank. Our previous boat was a 24' bayliner with a carbureted 5.0l merc and an alpha 1 drive. Not a lot of top speed but it got up on plane nicely. I assumed at a minimum this boat would perform similarly but with more top speed. Even though it is an extra 4' it has a fuel injected 5.7l with a Bravo 3.
 

QBhoy

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Mar 10, 2016
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It is a Bravo 3 so dual prop. I believe it originally had 3 blade props and previous owner upgraded to the 4 blade. I will double check but I was told that the 22 pitch was correct for the boat. I don't believe we a carrying too much weight. Only 1/2 tank of gas, very little fresh water, and mostly empty waste tank. Our previous boat was a 24' bayliner with a carbureted 5.0l merc and an alpha 1 drive. Not a lot of top speed but it got up on plane nicely. I assumed at a minimum this boat would perform similarly but with more top speed. Even though it is an extra 4' it has a fuel injected 5.7l with a Bravo 3.
I’d maybe try and find out what other identical models like yours came with, prop wise. Usually bravo 3 drives are propped well from new. Not often there is the need to mess with the props. I’m not sure many would consider going from a bravo 3 set of original stainless 3 blades to 4 blades…an upgrade. Good chance she’s been fitted with after market cheaper and poorly suited props perhaps. Could be wrong, but mostly these bravo 3 are fitted with 3 bladed props and usually do a good job of it.
There may be a owners club or group you could ask others what they have ?
But I’d also say that most boats this size and with similar engines, would be on the verge of needing trim tabs full down to assist planing too.
Are you getting well into the rpm range when she does plane and full throttle ? You want to be in the very late 4000’s wot for sure. If not 5000 rpm.
 

jbied72178

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Aug 17, 2022
Messages
7
Thank you for your input. I will take any help and info i can get.
From what I understand 3 blade props get higher top speed but are slower to plane. 4 blade will help to get on plane but you'll lose some top speed. I could be wrong on that though. I will investigate which props are ideal.
With trim tabs full down it does help, but not too much.
When I'm leaving my marina I'm usually at 1400-1600 rpm and about 10 mph. When I go to WOT the rpm's only hit 2900-3000 and speed gets to around 15. It takes about 30 seconds for the rpm's to slowly climb to just over 3100 and speed to reach the low 20's. At that point the boat will start to plane and the rpm's will start to climb faster as well as the speed. You can hear a complete tone change from the engine as everything takes off. Then I'm able to start trimming the engine up to gain more rpm and speed. I've had the rpms up to 5000 and the speed over 36mph.
 

QBhoy

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Mar 10, 2016
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6,995
Thank you for your input. I will take any help and info i can get.
From what I understand 3 blade props get higher top speed but are slower to plane. 4 blade will help to get on plane but you'll lose some top speed. I could be wrong on that though. I will investigate which props are ideal.
With trim tabs full down it does help, but not too much.
When I'm leaving my marina I'm usually at 1400-1600 rpm and about 10 mph. When I go to WOT the rpm's only hit 2900-3000 and speed gets to around 15. It takes about 30 seconds for the rpm's to slowly climb to just over 3100 and speed to reach the low 20's. At that point the boat will start to plane and the rpm's will start to climb faster as well as the speed. You can hear a complete tone change from the engine as everything takes off. Then I'm able to start trimming the engine up to gain more rpm and speed. I've had the rpms up to 5000 and the speed over 36mph.
The behaviour between 4 and 3 blade you’ve mentioned can be true. But can also just as easily have exceptions too. 4 blades can often have a larger diameter and heavy things to spin up too.
But perhaps more relevant to your situation, it’s a very rare thing to have both props on a two or duo prop outdrive, to have both props 4 blade…and especially unusual on a bravo. Can’t think I’ve ever known a bravo 3 with two 4 blade props to be honest. They may well be fairly inefficient and or in effective and a detriment to each other in terms of getting a hold of things. When Volvo Penta produced a duo prop outdrive with a 4 blade. It was only one of the props that had 4 and the other 3 usually. To assist their diesel powered boats get going. The vast majority otherwise are most certainly 3 bladed. I’d be tempted to find out what you would have had originally and look at what similar type craft with similar set ups have. Like any other number of the 28-30ft Brunswick boats likely have. Bayliner 2855/maxum etc etc. find a few similar and see what they have. I’d be sure it’s likely very few, if any of them will have two 4 blades on their bravo 3 perhaps
 

jbied72178

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Aug 17, 2022
Messages
7
Thank you. I will definitely look into that. This has been driving me crazy because everything checked out good on the boat, it's just slow.
 

QBhoy

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Thank you. I will definitely look into that. This has been driving me crazy because everything checked out good on the boat, it's just slow.
To be honest there are lots of possibilities it could be otherwise. So many variables with such matters. Hard to believe for some, but I know that even the smallest of things can affect a boats performance quite drastically. Even in fresh water, my boats can lose 5-7 mph in performance between the start and the end of the season, just with fuzz on the hull. Anything at all to do with props have the most influence. Water is such a challenging thing for a boat to push through. As you’ll know I’m sure.
 

jbied72178

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Joined
Aug 17, 2022
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7
This is what someone on a Larson forum said:
Original ex factory on mine were 22p.

I’ve dropped to 4blade 21p front and 21p 3blade rear and it is now a different boat for hole shot

So you may be on to something for sure. The previous owner gave us 2 other sets of props when we bought the boat. A set of 20 and 22 pitch 3 blade props (assuming the 22s are the originals). I will be swapping to the 3 blade as soon as I can. I will keep you posted. This is the most promising solution I've had.
 

QBhoy

Admiral
Joined
Mar 10, 2016
Messages
6,995
This is what someone on a Larson forum said:
Original ex factory on mine were 22p.

I’ve dropped to 4blade 21p front and 21p 3blade rear and it is now a different boat for hole shot

So you may be on to something for sure. The previous owner gave us 2 other sets of props when we bought the boat. A set of 20 and 22 pitch 3 blade props (assuming the 22s are the originals). I will be swapping to the 3 blade as soon as I can. I will keep you posted. This is the most promising solution I've had.
Good luck. I’d try everything you have for good measure and comparison! Good luck
 

Scott Danforth

Grumpy old guy who plays with boats
Joined
Jul 23, 2011
Messages
41,999
-Prop is correct: 22p 4 blade
-Engine trimmed down fully
-Trim tabs up or down make little difference.
-Once on plane the rpm's and speed take off: can get 4600+ rpm and 35+ mph
-Not overly loaded boat. Little fresh water in the tank as we use city water hookup at dock. Waste water emptied regularly. And 1/2 tank gas.
- checked fuel pressure and is good: 43psi at WOT
- checked compression and its good: 148-154 at all cylinders
-fuel injectors cleaned and good
-new plugs, wires, cap, and rotor

I wasn't able to be at the survey/sea trial when we purchased the boat. My wife went to that but can't remember if the boat performed better or the same as it does now. So I'm not sure if there is an issue or "that's just the way the boat is".
Drop your pitch .
 

tpenfield

Supreme Mariner
Joined
Jul 18, 2011
Messages
16,075
Well, to start the boat is under powered. You probably would have noticed that on the sea trial. I'm not sure why manufacturers under power their boats (at the base model), but they do. - Saves a few $$$ on the selling price, I suppose.

The dry weight of the boat is spec'd at 6,000 lbs. and the engine is 300 HP, which is good for a 5.7 L

The boat is fairly light for its length, but still a single 5.7 L engine vs. a 27-28 foot boat is out-matched.

A couple of things you could do . . .

1) See if you can verify the actual weight of the boat (removing all the gear and having as little fuel/water in it as possible). Head off to the truck or waste recycling scales. If the weight proves to be a lot more than the spec'd "dry weight" then you may have to look into what may be causing that.

2) Go down to a 19" or 20" pitch propeller set and see if that improves things. (Is it a dual prop or single prop outdrive?)

3) Remove any excessive gear from the boat, or possibly locate more of the gear forward.
 
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jbied72178

Cadet
Joined
Aug 17, 2022
Messages
7
QBhoy Thank you! Looking into the props i found that the previous owner installed Signature Props from Hill Marine. They are a 4 blade set for the forward and aft props. But you have to go down in pitch for them to work properly. He did not do that. He stayed with 22 pitch that is the original pitch for the boat. He had given me the original set of props when i bought the boat. So I swapped the aft prop to the original 3 blade today. I can't believe the difference it made! It was a completely different boat on the water. Went from a dead stop to on plane in 14 seconds. Thank you to all for your help. I've been working on getting this right all summer. Unfortunately the boat comes out in 2 weeks for winter storage. But at least I know that it's fixed and ready to go for next summer.
 
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