Concave hull / Low RPM

[BigD]

Hello all. New guy on the block here.

I purchased a 1989 Reinell 215C OMC 350 260 HP a couple of months ago. I've been trying to find out why I can't get above 3800 rpm 38 mph GPS with a 19 pitch prop or 4150 rpm and 37 mph with a 17 pitch prop. Engine runs fine up to the above speeds then just stops there.

I just noticed a couple days ago that there is a concave area in the starboard strake located at the front half of the trailer bunk. This concave area is approx 34" long and 1/8" deep at center and is fairly uniform. The aft end of this area is 26" ahead of the stern/transom. Can anyone tell me what effect this might have on the boats performance?

Thanks,

BigD

[BigD]

Does this post belong in the Design / Powerboats forum rather than Open Discussion?

[mackid068]

Yes, and that's where it is. The concave area is probaby la natural feature of the boat, so there's not much that it'd be worth doing (contact previous owner to see if any modifications were made). Look at the manual if it's there.

[BigD]

Thanks mack. Would a patch stick if I ground down the hull, slapped it in and smoothed it out?

I probably should do something to get the load off the engine if I can't smooth out the hull. The selling pitch of this boat was "engine was rebuilt and new block installed 250 hrs ago". I think I know why now. There is only 650 hours total on the boat. Maybe I'll have to go even smaller with the prop to get the WOT rpm's in the 4600 or so range. Sure hate to lose the mph but better than trashing the engine.

[mackid068]

I honestly don't know. Powerboat's aren't my area, but I would think that less RPMs, if it means not trashing an engine, is good.

[cyclops]

You can gain speed, raise RPM, lower the load on the engine and burn less gas by trying different loaner props from a good prop shop in your area. The right prop does everything best.

[BigD]

I don't know if re-proping is the answer here. We're talking about a boat and drive train that should be making around, if not over, 50 mph at 4800 rpm with a 14.5 x 19 three blade prop. It would seem that either the irregular hull on the starboard side is causing excessive drag or the engine just has no b__ls. Maybe try a full carb tune up before going to the expense of having the bottom of the hull made true?

Any advice or thoughts on this matter are appreciated.

Thanks

[stevel]

You can keep the boat down to speeds where the hydrodynamic loads are not a problem, but that's no fun, is it? If everything else about the boat is to your liking, it would be worth doing.

Back in the day when I worked in a boat shop, we used to straighten out the bottoms of boats all of the time. The problem is that you will have to empty the tanks, pull the engine, and take out anything else that is heavy. Once you have done that, you will need to flip the hull to build up the low spot.

The patch will stick if you grind the area first. We used resin, but I'd bet epoxy would stick even better. You will need to make a topographic map of the low spot using a long straightedge. Once you have done that, lay up one layer of glass in the lowest spot. Then you go over that with larger layups until you have filled the entire low spot. After that you grind everything smooth paint the patched area and put your boat back together.

The process of building up the low spot is more challenging than it sounds, which is the reason that shops get a lot of money for doing it. If you want to do it, I'd be happy to go into more detail about the procedure. Just let me know.

[BigD]

Sure appreciate the post steve. This is the kind of info I had hoped to find. I'll check with a couple shops in the area that work with fiberglass bodied cars and see what they can do ..... and of course show them your information. More detail would be great.

The county population here is about 4,000, so no boat shops within a couple hundred miles. However, I may be better off towing the boat to the "big city" to see about getting this done by an experienced boat shop instead of using an auto body shop. What do ya think?

[mackid068]

Are you SURE that it's not a natural curve? is it just too big? I don't think that a small fiberglass mistake/damage would keep your speed so low. Maybe an engine issue?

[BigD]

There is not an indentation like this on the port side. Port side is smooth and straight so I believe it is not there on purpose. As far as the speed reduction, I was comparing this indentation to the dropping of a trim tab and the effect that would have. The steering is kind of squirrly, but it runs nice in a turn in either direction ..... I have a couple more things I will check as far as engine performance and I will have that ruled out or find it is the cause.

[stevel]

It is definitely worthwhile to check out the possible prop and power-related problems, and to compare your hull to another of the same model that is performing up to spec. The concave area isn't a good thing, but may not be the entire problem either.

[stevel]

Since I'm at work right now, I don't want to take the time to go into the details of the bottom repair. I'll post some more on that in a day or two.

[woodboat]

Are you SURE this particular 350 is not within it's power curve? My 260 HP, 350 marine power is propped to run 4100 WOT. The fact that you reduced pitch, RPMs went up yet top speed drop 1 MPH suggests that this particular engine is right at it's designed MAX rpm. If this is like the Reinells I remember they were a little heavy, very deep V, kinda looked like a sea ray. They sucked a lot of power and in general ran in the mid 30's WOT. One would think that a concave area would push the bow over a bit. If it isn't flopping to one side while running there is a good chance it is on purpose.

[stevel]

I've reread the thread to make sure that I'm not going too far astray. I think 38 MPH is actually pretty good for a 350 in that boat.

As for the concave area, Woodenboat is correct that it would push the bow over as soon as it started having much effect on the performance at all. If it is not quite close to the centerline, it would also make the boat flop over on that side. You may have pegged it when you said that it would be like having a trim tab down. This may be some built in trim to counter prop torque.

On the other hand, it may be a warp from pulling the hull out of the mold too soon, or it could even be from the boat sitting on an ill-fitting trailer for an extended period of time.

I'd try Googling to find a Reinell forum and compare performance notes with people who have the same hull.