Solutions to excessive planing speed

[CChase86]

Re: Solutions to excessive planing speed

Yes, that's a good point about the speed. The speed was with a GPS, although the speedo on the boat can be accurate, it certainly isn't many times.

Can anyone confirm what speeds they stay on plane with on a 17-19 foot boat with a 4.3 I/O, just so I can confirm that 22 mph is high? I think that might be a good starting point.

 

[CChase86]

Re: Solutions to excessive planing speed

Put hydros back on. go to lowes and get a few bags of play sand and move them around on boat to get the right cg. "center of gravity". Wetjets were really bad about porposing, now they have bladder that can be filled in nose of jet to fix problem. If outboard, 'jack plate'! A LOT depends on swell or wave conditions.

I will try moving weight around in the boat but I'd really like to avoid the hydrofoil if at all possible. Maybe there is no easy other solution.

I'll post back after this weekend.

 

[180shabah]

Re: Solutions to excessive planing speed

Don't for get to check the hull for straightness. It only takes about 5 minutes and doesn't cost a penny (if you have a straight edge, 4' level works good for this).

 

[CChase86]

Re: Solutions to excessive planing speed

Don't for get to check the hull for straightness. It only takes about 5 minutes and doesn't cost a penny (if you have a straight edge, 4' level works good for this).

Straight in which dimension?

 

[180shabah]

Re: Solutions to excessive planing speed

Straight in which dimension?

See above and below....

Next verify the running surface - from the transom forward the first 4-5 feet should be straight and flat. Any hook(concave) or rocker(convex) will drastically affect performance.

If you go to the adults only area, you can download one of the Mercruiser engine manuals. it doesn't matter which one so get one of the smaller ones. In the first section of each it discusses basic boat term and issues, including hook and rocker. It has a drawing of each you can look at.

 

[SuzukiChopper]

Re: Solutions to excessive planing speed

Just to be a little more methodical, this is what I'd do:

1. Try different trim settings first.
2. Try moving some weight to the bow.
3. Try different trim settings with the weight moved.
4. If you still aren't happy, call the folks at Nauticus (smart tab people) and have a chat with them. I'm quite sure they will have the answers on whether or not their product will work. From what I've seen, they don't try and sell you their product if it won't work for your application.

A little phone conversation could go a long way in this case.

 

[nlain]

Re: Solutions to excessive planing speed

Before I put Smart Tabs on my boat, 04 185 4.3L, if I dropped below 20 I would start bogging down, with Smart Tabs I can get down to about 14 before I have to start watching the throttle. Smart Tabs I think will help your boat since they will give lift to the stern and when you trim up there will be more boat out of the water. But do all the basics first.

 

[MikDee]

Re: Solutions to excessive planing speed

His boat has built in trim tabs in the hull already, look at the picture

 

[nlain]

Re: Solutions to excessive planing speed

I saw the picture and I still think they would help. I could be wrong so not gonna worry too much about it. I do hope that John sees this thread I would like to have his input on this one.

 

[QC]

Re: Solutions to excessive planing speed

His boat has built in trim tabs in the hull already, look at the picture

How are fixed extensions of the hull trim tabs? They are not "trimmable" and they are flush to the rest of the hull.

 

[MikDee]

Re: Solutions to excessive planing speed

How are fixed extensions of the hull trim tabs? They are not "trimmable" and they are flush to the rest of the hull.

The 18" extensions of the hull past the transom are made to help the boat get on plane, & keep it on plane. No, they're not adjustable trim tabs (per, se). They do create extra drag for that reason, especially when you go to trim out at WOT, (IMO not the best hull design, from my experience ) but, you've got to work with what you've got! Adding trim tabs is just adding even more drag, that's why I personally don't recommend them for this hull design. With the engine package moved forward 18", I am very surprised he has any issues with getting on plane at a low speed, or keeping it, on this boat. I bet the trim of the drive is very critical to the operation this boat as well. I also think this design is prone to porposing at times, more then a conventional hull.

 

[SuzukiChopper]

Re: Solutions to excessive planing speed

The 18" extensions of the hull past the transom are made to help the boat get on plane, & keep it on plane. No, they're not adjustable trim tabs (per, se). They do create extra drag for that reason, especially when you go to trim out at WOT, (IMO not the best hull design, from my experience ) but, you've got to work with what you've got! Adding trim tabs is just adding even more drag, that's why I personally don't recommend them for this hull design. With the engine package moved forward 18", I am very surprised he has any issues with getting on plane at a low speed, or keeping it, on this boat. I bet the trim of the drive is very critical to the operation this boat as well. I also think this design is prone to porposing at times, more then a conventional hull.

This is why I suggested giving the manufacturer a call and asking for their opinion. They make them for jet boats with the same type of hull so I'm sure they know what they're doing.

My thought also was that there actually might be enough room to mount the tabs on the inset part of the transom without interfering with anything (maybe using a smaller then recommended set). That would eliminate mounting them on the pods.

 

[QC]

Re: Solutions to excessive planing speed

I guess my concern is that regardless of whether it is soaked foam, weird f'ed up hull design, rocker, a hook, underpowered, over propped, under propped, or the operator has issues, the fact is that trim tabs (helm adjustable or SmartTabs) will reduce his planing speed significantly and that is what he wanted . . .

 

[SeanMcl]

Re: Solutions to excessive planing speed

If I'm not mistaken, all the hulls I have seen with this design have those "hull extensions" raised up somewhere in the range of 3 to 6 inches above the bottom of the hull. The idea being that when you get up on plane, the extensions are not dragging in the water. When the bow rises, then the extensions contact the water and push the bow lower.

I don't know if this is the case here, but judging the year of the boat ('95), I'd bet it is. How this would affect the trim tabs themselves, I also don't know, but I a quick call to Nauticus would tell you it they recomended them for this hull design.

Just my thinking on this is, if he's got hull extensions of somewhere in the 18" range (my guestimate based on the pic) acting like 18" fixed trim tabs and his planing speed is still high, that there is some other issue affecting his planing speed. CChase86 mentions that he gets on plane just fine, so perhaps this is just the way this particulat boat handles. Maybe ask in the owners forum for others experiences with similar boats.

I don't think I would put tabs on if this was my boat until I had checked everything else out first. He's checked the foam; maybe check the weight of the boat with a full gas tank, passergers and gear; is it possible for the outdrive to be misaligned; is the hull warped; stuff like that.

 

[coastalcruiser]

Re: Solutions to excessive planing speed

I guess my concern is that regardless of whether it is soaked foam, weird f'ed up hull design, rocker, a hook, underpowered, over propped, under propped, or the operator has issues, the fact is that trim tabs (helm adjustable or SmartTabs) will reduce his planing speed significantly and that is what he wanted . . .

+1
get some small tabs on there!
"once you got that you'll never go back"

 

[Hitech]

Re: Solutions to excessive planing speed

I had the same issues, all of them. My boat is certainly different, but Smart Tabs fixed every one of the problems listed by the OP.

Smart Tabs do much more than fixed extensions could ever do. I'd bet that planning speed will be lower on the OPs boat with Smart Tabs.

I'd probably make a quick call, but only to confirm that they believe that Smart Tabs will work with his boat.

 

[CChase86]

Re: Solutions to excessive planing speed

Well I spent about 10 or 12 hours out this weekend screwing around with throttle, weight placement, and trim.

What I found was that, if the boat was relatively empty (just me and 9 or 10 gallons of gas) and the water "calm" I could keep the boat juuuuust on plane at about 18-19 mph and engine speeds at about 2200-2300 RPM.

I also wanted to confirm that the boat was otherwise operating properly. Specifications say top speed should be 45-48 mph at 4200-4600 RPM at WOT. I confirmed with GPS that top speed is 48.3 mph at 4500 RPM at WOT into a 5 mph headwind and relatively calm water (light chop).

So it appears that there's nothing "wrong" with the hull, and if I want to reduce the planing speed that trim tabs would be my best option. However based on some of the replies here I am thinking I will just try to make due with the speed as is, I may be able to lower it slightly with someone sitting up front.

Thanks again for everyones advice and comments.

 

[Capt'n Chris]

Re: Solutions to excessive planing speed

I think he's talking about a hook or rocker in the keel. A rocker could cause a problem like that. A mal-adjusted trailer is a 'kiss-of death" to a hull.

Captain Chris

 

[Jdeagro]

Re: Solutions to excessive planing speed

Please excuse the delay in posting. I don't look at the private Messages often ( not sure why - I just forget) and was directed to this thread.

Thanks for bringing this thread to my attention. I think there is a misunderstanding of the amount of lift that Smart Tabs provide when the boat is at cruising speeds.

The extensions on each side are there to create the effect of moving the engine forward in the hull, and changing the axis point. This should provide better balance and therefore better performance. I am not a hull design expert but using Smart Tabs to address the issue created by the unbalanced design (which may be the reason the extended the sides in the first place) can not hurt the performance. What seems to be the misunderstanding is that the extra lift from Smart Tabs is limited to the resistance (pressure) of the actuator, because the actuator travel is more than that required to bring the plate to level. In other words the plate can retract beyond horizontal. With this capability you can adjust (choose) the exact amount of extra lift required to eliminate the porpoising. A hydrofoil is rigid and will increase the lift more and more as the speed increases. This is why they usually reduce the top speed. They lift the stern and drive the bow down. If the hull design is like the one in the pictures, he may be able to mount the tabs on each side of the out drive. The SX series is 9.5" wide.