Improving a heavy under powered boat

Avalanchediver · Nov 11, 2003

Ok, I need some suggestions. The boat is a 1988 Formula 26PC with 7.4L Bravo1. When I load her up with three guys and all our dive gear, it is all she can do to stay up on top of the water. Keeping tanks and weights forward helps but she has to run 3600-3700 rpm to stay

on top of the water. Empty, WOT is about 4500rpm so the pitch is correct for the original Mirage prop. My main concern is being able to cruise easier with a big load. What do you think I should change. Bravo 2, Bravo 3, just a prop? Changing engines is not going to be an option unless I find a heck of a deal. Thanks for any suggestions, Eric P

crazy charlie · Nov 11, 2003

Re: Improving a heavy under powered boat

I would try going with a larger "working" prop.You will loose top end speed,but you will get on plane much easier and stay there.You may even see if you have the room for a doel fin or sting ray.Charlie

MarkJSullivan · Nov 11, 2003

Re: Improving a heavy under powered boat

Do you have a Steel prop or Aluminium prop?

cobra 3.0 · Nov 11, 2003

Re: Improving a heavy under powered boat

I'm with Crazy Charlie. Get a hydrofoil. Also, although a more costly solution could be putting on some trim tabs.

Avalanchediver · Nov 11, 2003

Re: Improving a heavy under powered boat

I forgot to mention, I havebeen running with tabs at about 90% down when heavily loaded. Also have not seen much success with biger props on Bravo 1 drives. I you have a specific prop in mind I would love to hear about it. I was hoping somone on the board may have switched from a bravo1 to a bravo 2 or bravo 3 and be able to give me the insight on the performance change they experienced. Eric

crazy charlie · Nov 11, 2003

Re: Improving a heavy under powered boat

I would consider a 4 blade if you dont think a bigger prop will do it.Charlie

Avalanchediver · Nov 11, 2003

Re: Improving a heavy under powered boat

I dothink bigger is better...but seems like I need a Bravo 2 to go bigger. A 17P mirage is a pretty big prop. Four blade might help.... I don't know what is availible in a four blade designed for power rather than speed. Eric

johnkc · Nov 11, 2003

Re: Improving a heavy under powered boat

you should prop the boat WITH the full load not empty.and check out a 4 blade prop. 4 blades are usually a stern lifting prop

tylerin · Nov 11, 2003

Re: Improving a heavy under powered boat

I have a five blade "high five" prop and I get good results out of her. It's not cheap but in comparison to a drive change, its cheap

Tabman II · Nov 12, 2003

Re: Improving a heavy under powered boat

Avalanchediver, I am Thomas and I work for Bennett Marine in the Client Service department. We have been supplying Formula with trim tab systems for quite sometime now, so you most likely have one of our systems installed on your vessel. Please take a look at your trim tabs and let me know what their size is and also what your Available Mounting Area (determined by starting 3-4 from the chine and measuring to within 8 of the outdrive), so we will know how much room you have to work with. With this information, you may be able to increase the overall size of your trim tabs, which will make your trim tab system more efficient (more overall trim tab area = more lift). In fact, you may be able to just replace the trim plane assemblies without moving the actuators, so the refit could be a very easy upgrade for you! Please give it try and get back to me with your findings! I look forward to your reply. Sincerely, MJ Thomas Bennett Marine, Inc. Client Services trimtabs@earthlink.net www.bennetttrimtabs.com

Avalanchediver · Nov 13, 2003

Re: Improving a heavy under powered boat

Thomas, The Tabs are 11X14 inches. They are within two inches of the outer chine and end within two inches of the inner strake. The hull also has a very noticable hook built into it by Formula to aid in planning. My problem is not the initial time to plane but rather the ability to stay planed out without running almost wide open throttle. She will stay on top at 3300rpm with out the dive gear. With the dive gear she needs 3700-3800rpm. To mich to runn that way to far. I know a bunch more horsepower would solve the problem, but I don't want to buy a whole new motor. I am hoping the increased efficience of a bravo 2 or a bravo 3 will give the boat just enough help. What do you think? Eric P

Bondo · Nov 13, 2003

Re: Improving a heavy under powered boat

You should be able to hang Much Bigger tabs on a 26' boat........ I'd think the Largest Possible Tabs,+ the Bravo III Should Really Wake Up your Boat...... Thomas will help you squeeze a Big set on there....

Tabman II · Nov 14, 2003

Re: Improving a heavy under powered boat

Avalanchediver, Ok, we have two (2) more inches to play with on the outboard side, so that will get us to 16 x 12's. On the inboard side we need to consider how close we are to the out drive, since we need to stay at least 8" away from the centerline of it to ensure we don't vent the props. Please take a look and let me know how much we have to work with as soon as you can! I look forward to your reply T II Bennett Marine, Inc. Client Services trimtabs@earthlink.net www.bennetttrimtabs.com

Avalanchediver · Nov 14, 2003

Re: Improving a heavy under powered boat

I would say you have a maximum of two inches on the inside. Not a propeller problem but rather a strake problem. The bottom of the boat goes flat for the strake and then angles down to the center of the V. I would have to remount higher and loose some of the tabs efficiency to go any larger. Eric P

Bondo · Nov 14, 2003

Re: Improving a heavy under powered boat

Eric, You've Already Got an Efficiency Problem...... Raise the tabs,+ go Much Bigger, If you want to Fix the Efficiency of the BOAT.....

SS MAYFLOAT · Nov 15, 2003

Re: Improving a heavy under powered boat

Avalanche, I have 27' with a 5.7. I'm really underpowered. I increased/decrease prop size, went to larger tabs, and even went with a new carb. My main problem was some of my floatation compartments that were foam filled were saturated with water. Once I removed the old foam, it reduced the weight of the boat tremendously. I would check to see if you have any compartments that are compromised. Changing your outdrive to a different model? I don't see where that would benefit unless you increase the hp of your engine. If your wanting to spend the bucks, I would consider a blower. SS

Tabman II · Nov 15, 2003

Re: Improving a heavy under powered boat

Avalanchediver, Ok, 18 x 12's sounds like the answer the correct size for you to fit. Please tell more about how you drive her and how fast she can run, since both areas will help us decide if you should use 18 x 12's w/1" Up Fins on the sides (stiffens the Chord length) or 18 x 12's w/3" Drop Fins on the sides (increases overall performance of given size trim tab, more lift). I look forward to your reply. Sincerely, MJ Thomas Bennett Marine, Inc. Client Services trimtabs@earthlink.net www.bennetttrimtabs.com

Avalanchediver · Nov 15, 2003

Re: Improving a heavy under powered boat

Cruise speed is 23 mph. Top speed just over 30mph. I like to cruise on plane as eficientlyas I can as far as RPM. Unfortunately, the engine is slightly into the 4bbl as I reach 23 mph witch is my slowest cruise on plane. Eroc P

Tabman II · Nov 17, 2003

Re: Improving a heavy under powered boat

Avalanchediver, Ok, if all the numbers are correct, then you should be able to install a set of 18 x 12's and order them with the 3" Drop Fins too! This way you will have as much lift achievable with the 18 x 12's, so you can hold her on plane as slow as possible. The part number you should shop around your local marine dealers, catalog &/or Internet retailers is TPA1812DF, which will retail for about $130.50 each. Please give them a call and let me know how it turns out! I look forward to your reply. Sincerely, MJ Thomas Bennett Marine, Inc. Client Services trimtabs@earthlink.net www.bennetttrimtabs.com

Improving a heavy under powered boat

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