Discussion in 'Stabs, Tabs & Gyros' started by HaveADay, Jun 1, 2016.
Will a Frigibar filled with beer on the bow help?
Don't make more mistakes to make up for the ones you've already made. You added a bunch of stern weight so the first thing you know of all of this is that you'd need a different prop. Until you get it propped right, don't start making other changes. One thing at a time.
What do you mean a naval architect was consulted? Did they design the addition or does this just mean you casually spoke to one. I can't imagine a naval architect who would tell you adding that weight wasn't going to change anything. If he did, then tell him to now correct the situation.
I can tell you why Seakeeper is stand offish. They don't take installation responsibility. They have authorized dealers who will. Did you work through their Chicago sales person, Bryan Billic?
Regardless, I wouldn't touch tabs, I wouldn't change anything until I tested some different props. Hopefully there is a local prop shop that will let you try some different ones.
One problem on installations such as this is that lowering the stern 2" may mean nothing on some boats, but 1" may be very significant on another. Realize among other things when you raise or lower the stern it's quite common for the trim tabs to require adjustment or raising or lowering. You lowered where they are.
I'd really recommend finding a good experienced shipyard. You aren't demonstrating the experience necessary for what you've undertaken. I wouldn't have it either, so not being critical, just observing.
Returning them to what spec? I don't like to prop a boat from a computer in an office. A sea trial using someone with running gear knowledge is my preference. That person is usually me. I can't tell you how many times I've had owners talk up how they had their props 'computer tuned' with who knows what for input data. You know the term ...garbage in, garbage out.
Adding fuel on the bow is the worst idea of all the fiddling you've mentioned. Especially if you're implying that this would be instead of using the aft tank. Regardless, weight distribution is a tricky business. Adding fuel capacity is even trickier because the weight changes. You are going down a rabbit hole here. I don't see where you mentioned how many RPM you lost. Back off some pitch, see what that gets you and go from there.
A new naval architect first.
I have added a 1" or so spacer (I had the yard do it) on several boats and it made a significant impact on trim on boats that needed it. It was cheap, thick starboard blocks with the mounting holes drilled in them. I would go in this direction. Every Carver I've ran needed ALL tabs fully down to perform and could have used more tab. I'd go this route first, then take 2" pitch out of the props. Any weight you can remove from the stern and get as far foward as possibly helps greatly. Losing any weight out of the stern also helps greatly.
As for the props, it sounds like a shop custom tweaked them to get them where they were and the work they did was right (added more camber near the hub for lift) and the speed you had and your prop shop took them back to a traditional shape losing the extra lift the last shop put in them. I've had Arneson and other props tweaked and the camber changed in different area's to get the boat to perform differently.
A naval architect ran calculations for the shock and static loads the seakeeper would transmit to the hull. The fabricator who made the bracket the stabilizer is installed on was working with him on another project and had him do the calculations for this. The focus of the work was around insuring the the forces that were transmitted to the hull were transmitted in such a way they didn't threaten the stringers or transom.
Indeed, I did work with Brian Billic on the install.
While I agree with you on one thing at a time I don't agree it makes sense to start with changing the props. Changing the props is the most expensive option available and determining how much pitch to remove is based upon how short of RPMs the engines are turning. On my boat, which requires a lot of tabs to begin with, it makes sense to attack trim and have the boat running flat before spending the money to change the props and then end up changing them again. Changes to the tabs are relatively cheap compared to the props.
In Chicago I am working with the yard who performed the installation who is also the most experienced yard in the city. On the great lakes our options are a little more limited.
That said, I agree that I don't have the experience to fix this. I am, however, the one writing the checks on this and the one who needs to be able to spend the money so I'm trying to make sure that I know enough to be an informed consumer. Hence I came here.
Thanks, I will try the spacer or block approach. I had wondered about that possibility previously and am intrigued to hear you've had success with it.
I don't believe they were custom tweaked, though I am relying on what i was told by the most recent shop. The propscan report showed the face camber as all over the place and highly inconsistent blade to blade and prop to prop. To the point that I can't imagine it was done intentionally by anyone.
What does the yard you're working with recommend?
Changing the props may be the most expensive but it's also inevitable. However, I was recommending trying some different ones before paying if you could find a prop shop that would work with you. The naval architect's focus, per your words, was the structure and stringers, not the change in weight or weight distribution. Changing the tabs will allow you to change the running angle and that certainly will be beneficial. I still think after that you'll need to change props.
My apologies if I've given the impression I don't think I'm going to need to modify the props. I expect I will. I want to sort the other items first so that I have the data about how far up I'm able to turn the engines. If I'm within 40-50 RPMs it's a different ballgame than if I'm seeking 120 RPMs. Thus far the shop doesn't think they have props in stock in the correct dimensions for me to try. Another downside to this market is that there are relatively few bigger boats and hence fewer support services than Fort Lauderdale.
The yard is recommending the approach we are taking right now.
120-150 rpm isn't that far off and if the engines are electronically controlled, it's better to be low on turns rather than run into the governor when estimating prop changes. I'll side with the group recommending correcting the wheels as a higher priority and as you say, inevitable. Your engines are making all the power they can now and while they aren't getting full WOT rpms, correcting the props will more than likely do nothing to top speed, all you will be doing is changing what speeds you make at what rpm. Just as an example say you're making 23 knots at 1900, after taking out 2" you'll make that same 23 knots at 2050 but will be able to achieve 2350 WOT so your engines are not overloaded. You may get some trim changes by playing with tabs and weight distribution but they will likely not affect speed or engine rpms very much.
Okay, so wheels are in motion on a few items. I'm waiting for the prop shop to give me a call back on timing on pulling some pitch out of the props as well as the possibility of any I could try with less pitch in them.
Also, I've been brainstorming quite a bit about ways to move weight around on the boat and have moved some smaller items around like tools and spares but fear I've probably only moved 150 or so pounds. One idea I had... along the lines of the fuel tank under the forward bunk, what if instead of a fuel tank I put a couple of water tanks or bladders. My fresh water tanks are currently outboard the main engines. So, the weight is aft of the center of the boat but pretty close to the mid point as well. If I put 100-120 gallons of water in bladders I would have the option to reduce the amount of water in the main tanks and hence shift weight forward. The water doesn't come with much of a liability in terms of leaking or smell issues. I could put in a pretty simple manifold in the engine room that would allow the fresh water pump's source to be selected between the bow tanks and the main tanks. I am having a hard time seeing much in the way of downsides. This would give me some adjustability and allow me avoid increasing the overall weight of the boat by just managing how full I keep the respective tanks. Thoughts?
Bladders are certainly a viable option to move fluids but they should be done "right". I recommend using ones custom made to fit the coffin they are going in, and that coffin has to be strong enough to support the load. "Pillow", or empty bag bladders can have sloshing issues but there are porous foam-filled ones available (for both water and fuel) that alleviate that issue. Be warned, they aren't inexpensive, last ones I bought ran about $14-15 per gallon for custom made but they will hold up. I use nothing but bladders forward of midships on our newbuilds but from experience (and measurements) I expect 10G impact loading in those areas. Here's a couple pics of a fuel bladder being installed in a coffin on a fast (47+ knot) 63 sportfish we built, it's being vacuumed down to shrink it. 8 years of service so far with no issues.
Those look like exactly what I have in mind There is already a good deal of structure in the bow that I think can be easily picked up to be sure we are spanning enough of the hull to spread the forces. I suspect that your boats are a bit more capable and are likely to see greater loads but I would still expect to see some pretty good shock loads in the bow.
I can't read the end of the URL, what brand of tanks are you using? The foam filled option seems like a very good one.
I've used these http://store.interstateproducts.com/products/Fuel-Bladder-Tanks and ATL, both with excellent results. (Hope that didn't violate terms Carl!)
Thanks much! Really appreciate it