Blast plate Question [Archive]

Dimarco21

02-15-2005, 11:33 AM

I have 1976 21' DiMarco cruiser. I get chipping on the bottom of my hull right in front of the rudder and the majority of it is on the center and drivers side. In 2 years I get a 1" X 2" section chipped out. It goes through the gel coat and is about 1/32" deep. I repair it with a couple of light coats marine tex and sand it smooth.
Is there any way to prevent this? I believe it's prop wash that is causing this. Can I add a aluminum blast plate to my hull like I see on other boats? I think it would have to be recessed into the hull, Will I lose hull strength by doing this? Thanks.

superdave013

02-15-2005, 11:39 AM

the same thing was happing to mine. The plates I had put on were stainless. And yes they were recessed into the bottom of the boat. Mine's pretty thick back there so I'm not worried about it.

wsuwrhr

02-15-2005, 06:22 PM

Hard annodized aluminum. Or stainless like SD stated.
I can make you one up if you like, give Billy B a call about the bottom work needed.
You need to clearance the bottom of the boat for it though.
Brian

wsuwrhr

02-15-2005, 06:28 PM

I dont have a picture of one uploaded into ***boat, when I get home i will post it
Brian

Dimarco21

02-15-2005, 07:11 PM

the same thing was happing to mine. The plates I had put on were stainless. And yes they were recessed into the bottom of the boat. Mine's pretty thick back there so I'm not worried about it.
I'm not worried about hull thickness (1" or so) either. Do you know if you have to re-gel the section of fiberglass I cut out? I would only router out the plate thickness but, does the fiberglass have to be resealed? Thanks

wsuwrhr

02-15-2005, 07:48 PM

I'm not worried about hull thickness (1" or so) either. Do you know if you have to re-gel the section of fiberglass I cut out? I would only router out the plate thickness but, does the fiberglass have to be resealed? Thanks
I don't know about regelling the bottom, I am just making the blast plates.
That is why I mentioned calling Billy.
Brian

VD CRUISER

02-15-2005, 08:01 PM

Kurtis500

02-15-2005, 09:30 PM

I'm not worried about hull thickness (1" or so) either. Do you know if you have to re-gel the section of fiberglass I cut out? I would only router out the plate thickness but, does the fiberglass have to be resealed? Thanks
No, it should be fine. The laminate you are exposing should be solid. Fiberglass doesnt require gelcoat as a barrier. Gelcoat is simply engineered resin.

Rexone

02-15-2005, 10:15 PM

Use stainless, aluminum will erode quickly from this cavitation. I've seen it go through stainless in extreme cases but it takes much longer.

Dimarco21

02-15-2005, 10:22 PM

I used stainless steel about .090" thick, and did not put any gel on the area I routed out. I put a thin coat of Marine Tex or Sea Goin putty in the recess before I secured the plate to fill in any irregularities. I also put some release agent on the plate in case I ever want to get it off. Sounds like yours is eroding in the same place as mine. I now have a erosion problem just in front of the plate. There was no problem there before I put the plate on. :confused:
VD, How large is the blast plate you made? You mentioned erosion problem in front of the plate now. I was going to make a stainless steel one about 12" X 12".
I am just making the blast plates.
Wsuwrhr, What do you think about tapping the fiberglass to install this plate, like most shaft logs are done? Less thru holes to leak.

wsuwrhr

02-16-2005, 05:08 PM

Wsuwrhr, What do you think about tapping the fiberglass to install this plate, like most shaft logs are done? Less thru holes to leak.
You mean putting threads in the fiberglass and not using thru bolts?
If I understand you correctly, I think your new blast plate will be at the bottom of the lake after awhile.
Just my opinion.
If you silicone the shit out of it you will be ok.
Brian

wsuwrhr

02-16-2005, 05:10 PM

Use stainless, aluminum will erode quickly from this cavitation. I've seen it go through stainless in extreme cases but it takes much longer.
I mentioned hard annodizing the plate, after the process the surface will be much harder than steel at that point.
Plain aluminum wouldn't last long.
Brian

schiada96

02-16-2005, 06:52 PM

This is how I make the blast plates for Schiada .125 stainless steel & formed to match the bottom of the boat.

coolchange

02-16-2005, 07:10 PM

No, it should be fine. The laminate you are exposing should be solid. Fiberglass doesnt require gelcoat as a barrier. Gelcoat is simply engineered resin.
But I think the glass requires a solid barrier or It will "wick" and turn white from moisture.

Dimarco21

02-16-2005, 07:13 PM

You mean putting threads in the fiberglass and not using thru bolts?
If I understand you correctly, I think your new blast plate will be at the bottom of the lake after awhile.
Just my opinion.
If you silicone the shit out of it you will be ok.
Brian
Brian, It was just a thought (maybe not a good one), I think thru bolts are the only way to go. I would hate to see that thing come off and take out my rudder.

Dimarco21

02-16-2005, 07:15 PM

This is how I make the blast plates for Schiada .125 stainless steel & formed to match the bottom of the boat.
Thanks schiada96, do you reseal the fiberglass after it's cut out and before installing the blast plate?

wsuwrhr

02-16-2005, 07:22 PM

Brian, It was just a thought (maybe not a good one), I think thru bolts are the only way to go. I would hate to see that thing come off and take out my rudder.
or the prop, or come up through the bottom of the boat.
Brian

superdave013

02-16-2005, 07:43 PM

I'm not worried about hull thickness (1" or so) either. Do you know if you have to re-gel the section of fiberglass I cut out? I would only router out the plate thickness but, does the fiberglass have to be resealed? Thanks
Mine was not re-geled after it was routered out. There is pics of it in my gallery on hotboatpics.com.

VD CRUISER

02-16-2005, 07:56 PM

Dimarco, not a real good picture, but you can get an idea of the size. The boat is in storage now, too far away for me to measure. Look closely its covered with speed cote.
http://www.***boat.com/image_center/data/520/1410100_1652.JPG

superdave013

02-16-2005, 08:51 PM

Here's mine
http://www.hotboatpics.com/pics/data/500/48strut_install-med.jpg
http://www.hotboatpics.com/pics/data/500/48strut_blast_plate-med.JPG
http://www.hotboatpics.com/pics/data/500/48strut_blast_plate1-med.JPG

Dimarco21

02-16-2005, 10:32 PM

or the prop, or come up through the bottom of the boat.
Brian
That would be a bad thing....right. LOL
Thanks guys. VD that plate is massive, and your still having erosion problems? I was think more like superdave013 plate size.

Scape Goat

02-17-2005, 12:14 AM

could one be done to a rounded bottum or is it to hard to contour?
http://www.***boat.com/image_center/data/500/59DSC01590-med.JPG

schiada96

02-17-2005, 06:05 AM

hey scape goat get that prop checked

wsuwrhr

02-17-2005, 07:04 AM

could one be done to a rounded bottum or is it to hard to contour?
http://www.***boat.com/image_center/data/500/59DSC01590-med.JPG
Flat bottoms will take the shape.
V bottoms will need to be preformed to the bottom of the boat.
Brian

wsuwrhr

02-17-2005, 07:05 AM

hey scape goat get that prop checked
I second that bud,
V-Drive Tom on the boards has the technology.
Brian

wsuwrhr

02-17-2005, 07:06 AM

That would be a bad thing....right. LOL
Thanks guys. VD that plate is massive, and your still having erosion problems? I was think more like superdave013 plate size.
SD's goes up far enough.
Should be a few inches in front of the prop too.
Brian

Tahiti350

02-17-2005, 08:51 AM

could one be done to a rounded bottum or is it to hard to contour?
http://www.***boat.com/image_center/data/500/59DSC01590-med.JPG
I'm not a V-driver, actually have a 1/2 whacker, but is that prop on the right way? :confused: looks backwards to me???? Is this the ultimate V-drive speed secret? :D :jawdrop:

superdave013

02-17-2005, 08:56 AM

I'm not a V-driver, actually have a 1/2 whacker, but is that prop on the right way? :confused: looks backwards to me???? Is this the ultimate V-drive speed secret? :D :jawdrop:
lol, maybe he could put an "inducer " in front of the strut like the jet boat guys. :D
Yes, that prop is on correct.

VD CRUISER

02-17-2005, 06:57 PM

Dimarco, as you can see it starts at the front of the cav. plates and goes up just past the prop blades. I ran it for a while after I made the strut change, without a blast plate and found that it was working on the bottom just in the area of the rudder. So I made a plate that would cover that area and maybe even catch a prop blade if it came off. Then after I put it on and tried my 2 blade it began to erode just behind the strut and at the leading edge of the blast plate. It is much worse with the 2 blade. Now I just patch it when needed. :cry:

steveo143

02-18-2005, 06:32 AM

Dimarco21

02-18-2005, 04:29 PM

Hi Philm steveo143 from LA. I'm going to route mine out from the rear of strut to the plate recess and use , .125 stainless. I plan to through bolt mine. I would just brush on some resin for piece of mind and seal with silicone or poxy putty. Finish with speedcote. What angle stut are you running? Mine was 8 degree before it broke and never had a problem in that area.
steveo dimarco 21 II
What's happin' Steveo, I think that's the hot ticket. I like the S.S. plate idea rather than using aluminum. I have 12 degree drop thru strut. We have another Delta run going (see hot spots west), interested?

Flatbroke 1

02-18-2005, 09:17 PM

This is the set up Sanger put on their boats. It sounds like what you are going to try to do. This one happens to be aluminum
http://home.ripway.com/2004-5/120571/blast_plate.jpg

Scape Goat

03-02-2005, 10:20 PM

that prop is history before I even bought the boat.
I would not run that piece to scarry looking.
Who could do the job on my boat if it came to it.
just currios for now
thanks brian

Kindsvater Flat

03-02-2005, 10:28 PM

Here is the mess under mine (old pic)
http://www.schoutenranch.com/miscboat/cavunder.jpg

superdave013

03-03-2005, 02:28 AM

that prop is history before I even bought the boat.
I would not run that piece to scarry looking.
Who could do the job on my boat if it came to it.
just currios for now
thanks brian
Prime Marine did a nice job on mine.