Z308 454MPI 25-55mph
 

Hello again fellow Mariah kin! :D

I am the second owner of a 2001 Mariah Z308, which has a single MerCruiser 454MAG MPI engine, MerCruiser Bravo Three drive with counter rotating props, all of which have only 78hrs total.

My latest question :shakehead: may be seen as a little dumb, but here goes –
My boat cruises fine & dandy up to 25mph at 3,300rpm, only requiring the usual trim to ease her bow down on plane, and to counter winds/currents etc.

My question comes when I take her above 25mph. The 2001 Mariah manuals tell us that the single 454MPI can push a Z308 onto 55mph. However when I take her beyond 25mph she increasingly leans over with the starboard side downward. Between 25-30mph I can mostly trim this out, but in reality I cannot take my Mariah above 25mph without her listing to starboard, no matter how much I trim.

I’ve checked my Bennett tabs are working, and whilst I appreciate weather and water conditions mean a lot, do fellow Mariah vet brethren have any advice? Are there any known trimming issues on a Z308 with 454 engines? Are there any things I should be doing or should avoid?

Thanks for all help and advice,
-Adrian

Re: Z308 454MPI 25-55mph
 

Re: Z308 454MPI 25-55mph
 

Adrian:
On my Z276MCC I have found that the deep V hull, along with the counter rotating props allow the hull to "settle" onto either the port or starboard side as you have described.
I am assuming your outdrive trim and trim tabs are in good working order and the boat load is at least close to balanced.

I like to begin trimming immediately after reaching minimum planing speed by first adding small amounts of up trim on the outdrive.... more throttle.... then small incremental adjustments on the trim tabs.....more throttle..... more up trim on the outdrive.....allowing a few seconds for the hull to settle between each adjustment.... and then periodically adding small adjustments either port or starboard trim tab as needed. The key for me is to trim early and often not allowing the boat to completely settle to one side or the other. After awhile it is second nature to reach up and tap the trim button as soon as I feel a little movement. Maybe after hitting a wake or a rolling swell from the side. Somtimes a little bump of the steering wheel in the opposite direction of the list will cause it to roll back it back on the proper trim.
I believe this is a common issue with counter rotating props due to the lack of "P" factor or prop torque that allows one to trim against the torque of the prop. It's kinda like flying a small airplane, trim and throttle.
Anyway, it works for me, I hope this helps!
Brit441

Re: Z308 454MPI 25-55mph
 

Adrian,

I agree with Britt, These are big boats and you just have to find the groove that your boat operates best at, using both tabs and motor trim. (If those trim tabs are working properly)

I start with mine completly extended, and then work back from there. We have twin engines so it's probably does not list as bad as single engine models.

Re: Z308 454MPI 25-55mph
 

Thanks Willy, Brit & Clinton (apologies I've forgotten you first name),
All your advice is appreciated.

Sure enough, when I build the speed in steps, trimming all the time, I can get closer to 30mph, but she always keels over to port or starboard as you get closer to 30mph. Now I never bought my Mariah for speed, and Puget Sound conditions mostly slow you below 25mph, but I will look at my outdrive and the power trim as you suggested Willy - Thanks

One item which may be a telling factor is the amount for engine trim I use. I fully utilize my working Bennett tabs, but I tend not to trim the engine up too much. Call this a naive question, but do you gents think insufficient engine trim upward when cruising may have her keeling over port/starboard? (spot the sailor in his first season as a power cruiser)

Thanks for all your time and guidance!
-Adrian :wink_thumbup:

Re: Z308 454MPI 25-55mph
 

Adrian:
On the Z276 when the outdrive trim is all the way down, the boat will list slightly to starboard. I slowly start trimming the outdrive up as speed allows. This usually will settle the boat to nearly centered or neutral position. then I add trim tabs a little at a time to fine tune the position fo the boat. It takes a while to get used to the process.
Just remember that the more trim tab adjustment you use, usually means less speed. If you have to really lower one of the tabs to get your boat to balance, you will not be able to optimize your boat speed. Tabs trimmed down equal more drag in the water. An outdrive properly trimmed up at the proper speed, equals less wetted surface and higher topspeed with lower fuel consumption. If everything is set-up properly, you should start with your trim tabs nearly parallel with the bottom of the boat. If your boat lists to starboard, the starboard trim tab should end up just slightly lower than the portside tab.
I spend most of my boating time in the CA delta and the San Fransico Bay. I think our boating conditions are similar and, although your boat is longer on the water line than mine, I think the hulls are of similar design.
When I get my boat trimmed properly it feels like it slips into overdrive. In rough condition it may be trimmed slightly nose down and in smooth conditions I trim the bow up a little and let'er fly!
Sorry if I am rambling on, but I really love these boats. I have also had sail boats(Santana 3030 and a Nacra 5.8) and various brands of power boats. I believe the original Mariah boats are the best looking and the best value on the water. If there was a better boat out there, I would buy it today.
Like my wife sez..."don't get him started or he'll never shut-up".

Good Luck!
Rick

Re: Z308 454MPI 25-55mph
 

Thank you Rick, I really appreciate your experienced guidance! :)

I certainly will try trimming first and primarily with the drive, then 'cleaning up' with the tabs if needed. I really appreciate your experienced feedback!

-Adrian :wink_thumbup:

Re: Z308 454MPI 25-55mph
 

Adrian, I'll second what Rick said. Think of it this way - when you have the trim all the way down, it's actually further than perpendicular to the the hull. While cruising, that will force the bow down. The water will want the least resistance possible, meaning a flat surface. In order to get a flat surface, the water will force the boat to list and ride on one side of the hull. If you trim up, less hull will be in the water and cause the boat to level out. Your tabs should almost not even be required above 25-30 (unless you're trying to "nose down" through chop). I think trimming up 1/2 - 3/4 will significantly reduce your listing issues.

Re: Z308 454MPI 25-55mph
 

Thanks Ryan, you 'Platinum Contributors' are teaching us newbie's a thing or two.

(I wont mention that I work for a certain aerospace company beginning 'B' on their Flight Controls, else I'll be showing how naive I'm being!) :rolling_laugh:

Re: Z308 454MPI 25-55mph
 

Like Adrian, I too am a newbie to boating but have experienced similar things to him with the my Z280. There is a noticeable list to the starboard side that I have been able to easily correct with a little upward trim on the starboard trim tab and a bit of a turn of the wheel to the port. However, when I was out on the Illinois River Wednesday with calm waters and no other boatrs, I had a severe list to the starboard side when I pushed the throttle almost all the way down. It was so bad that I had to back completely off the throttle to slow to a crawl. I should also point out that I had a full holding tank which I believe is on the starboard side while an empty water tank which I believe is on the port side and I was by myself i.e. 400 lbs on the starboard side and probably 50 lbs of water on the port side. When I accelerated in steps I did not experience this severe list again.

I was taken out by the Marina Service Manager when I took delivery of the boat a few weeks ago to show me how to operate various systems on the boat and how to drive it. He had me move the trim tabs all the way bow down before starting to accelerate to get on plane. I am still taking this approach, but when reaching about 3,600 RPM or so I then adjust the power trim up until the GPS speed maxes out and the engine sound is smooth. This puts the boat at about 27 mph with the bow splash about at the helm and the point where the wake crosses 15' to 20' behind the stern.

Having the trims tabs all the way down contradicts what you veterans are recommending but this configuration allows me to cruise easily between 27 and 30 mph compared to what Adrian is experiencing with his boat that I believe is similar in size but has more horsepower than my boat. So my question is whether having the trim tabs all the way down offset with some power trim up is more or less stable than having the trim tabs virtually all the way up as you folks suggest and rely primarily on the power trim?