How to get a boat rated for HP

[trendsetter240]

I have a 1971'ish Grew same model as Slickcraft SS170V. The boat had no plate with a rating on it when I bought it. It has been partially restored by the PO, the transom is new and the floor was replaced.

I know about the coast guard formulas, (L x W X 2)-90 and I know the original rating was between 100 and 115 HP.

I'm wondering if this is something that you can hire a marine surveyor for or if it has to be government? Am I stuck with the estimate I have based upon the limited info or is there some other option? Anybody ever had their boat re-rated?

Cheers~!

 

[4JawChuck]

In Canada...

In Canada...

That CG plate is meaningless in Canada, your insurance on the boat will be related to the size engine you hang on the transom and the length of the boat. Whether that engine is safe to put on your boat is up to you, seeking advice from a marine surveyor is probably a good idea but it is unlikely he will set himself up for a lawsuit by making a firm recommendation on the HP rating...however he can probably offer some good pointers.

I think the CG rating method is a good point to start as it has been derived from years of experience but 25 HP either way is not the end of the world...up here anyway. Engine weight is a big part of the formula and a 4 stroke weighs a lot more than a 2 stroke, be aware you may not be able to find 4 stroke CG ratings for older boats as they were not available back then. You can certainly find other owners of your brand/style of boat and get the CG plate data and go with that, your insurance will still be based on the HP and boat size, not a CG rating.

BTW this is a touchy subject on the board as it is a serious liability issue in the US and you likely would not be able to insure the boat if it exceeded the CG rating there, we do not have that issue...your the captain in charge mate.

For example I am upgrading my 80HP rated 16' Tuffy from 90HP to 200+HP, the transom and floor is being reinforced to handle the extra power as well as steering to hydraulic...my insurance should cost a fortune. The difference in weight between the two motors is 70 pds...batteries are moving up front to accomodate the extra transom weight and the on-deck portable fuel tank is going under the floor with a larger permanent custom tank. This is all legal in Canada as long as I am willing to take the risk and pay the extra cost for insurance, you can bet I am taking the extra time to engineer this upgrade carefully and will be taking her out in baby steps to ensure the boat is safe at speed.

I think you will find the maritime laws in Canada completely different from the US mainly because there are so many homebuilt fishing vessels in service and the HP rating is non-existant, therefore it is up to you to operate and rig the vessel safely...ultimately safety is your responsibility anyway.

 

[trendsetter240]

Re: In Canada...

Re: In Canada...

That CG plate is meaningless in Canada, your insurance on the boat will be related to the size engine you hang on the transom and the length of the boat. Whether that engine is safe to put on your boat is up to you, seeking advice from a marine surveyor is probably a good idea but it is unlikely he will set himself up for a lawsuit by making a firm recommendation on the HP rating...however he can probably offer some good pointers.

I think the CG rating method is a good point to start as it has been derived from years of experience but 25 HP either way is not the end of the world...up here anyway. Engine weight is a big part of the formula and a 4 stroke weighs a lot more than a 2 stroke, be aware you may not be able to find 4 stroke CG ratings for older boats as they were not available back then. You can certainly find other owners of your brand/style of boat and get the CG plate data and go with that, your insurance will still be based on the HP and boat size, not a CG rating.

BTW this is a touchy subject on the board as it is a serious liability issue in the US and you likely would not be able to insure the boat if it exceeded the CG rating there, we do not have that issue...your the captain in charge mate.

For example I am upgrading my 80HP rated 16' Tuffy from 90HP to 200+HP, the transom and floor is being reinforced to handle the extra power as well as steering to hydraulic...my insurance should cost a fortune. The difference in weight between the two motors is 70 pds...batteries are moving up front to accomodate the extra transom weight and the on-deck portable fuel tank is going under the floor with a larger permanent custom tank. This is all legal in Canada as long as I am willing to take the risk and pay the extra cost for insurance, you can bet I am taking the extra time to engineer this upgrade carefully and will be taking her out in baby steps to ensure the boat is safe at speed.

I think you will find the maritime laws in Canada completely different from the US mainly because there are so many homebuilt fishing vessels in service and the HP rating is non-existant, therefore it is up to you to operate and rig the vessel safely...ultimately safety is your responsibility anyway.

Hey 4JawChuck, good to hear from another Canuck!

Yes, I know this is a contentious issue here, I'm usually on the side of the USCG rating especially if the boater has the rating on their boat.

I'm not looking to mount something crazy on my boat, just want to get an accurate safe rating so I know what I can look at motor-wise.

I know for a fact there are some 17ft boats rated for a 150hp and some rated for a 90hp. I use my boat on long trips (50 miles or more) frequently in the summer months and maximizing cruise speed and fuel efficiency are HUGE factors for me.

The USCG formula gives me about 115hp max but this is without any of the handling test for my specific hull. I've read through all the documentation they provide on the rating tests. Short of strapping on a larger motor and running through the USCG tests on my own I don't know how to get the safe rating.

I now have a chance to pick up a 150HP motor for a great price but don't want to do it without a proper test to ensure that I'm not risking safety in any way.

There must be some way that people can have their boats re-rated. All the hull modifications and upgrades I see on here, what do these guys do about determining max HP rating for their new hulls?

cheers~!

 

[4JawChuck]

Re: How to get a boat rated for HP

In your case I would research other owners to find a CG rating and go with that, perhaps someone else with a similar boat will chime in and share their knowledge/experience.

Have you considered contacting the mfg? I had to contact Tuffy to find my original hull rating as the CG plate was faded beyond recognition. They responded immediately and were very helpful, the original owner actually still participates on boat forums and contacted me through a PM.

The mfg is still in business, give em a call!

http://grew.ca/contact.html

 

[tashasdaddy]

Re: How to get a boat rated for HP

http://forums.iboats.com/showthread.php?t=191283

 

[RotaryRacer]

Re: How to get a boat rated for HP

I kinda have the oppostite situation.

I have a 150HP motor and I am looking for a boat to put it on. There is a Slickcraft SS170 listed locally for a really good price. I have a few questions.

Is the Grew that you have actually, verifiably the same boat as the Slickcraft SS170?

What is the width of the transom...as defined by the coast gaurd docoument tashasdaddy linked to?

What is the height of the transom? 20"?

The current owner of the boat local to me says that even with the 90 HP motor he has on it, it may be more power than neccessary.

That being said, I made some assumptions and ran through the calc:

L = 17
W = 7
Transom Height = 20"

(17x7x2)-90 = 148 ... 150 HP rating.

But, as has been said with assumptions....

Without an actual boat in front of me I can't be certain on this.

 

[180Fisherman]

Re: How to get a boat rated for HP

That 18 x 8 x 2 - 90 formula comes to 198 hp for me but my boat is only rated to 150. What gives?

 

[H20Rat]

Re: How to get a boat rated for HP

That 18 x 8 x 2 - 90 formula comes to 198 hp for me but my boat is only rated to 150. What gives?

that formula is only a VERY rough estimate. According to that that formula my boat is rated for a max of 125. The SMALLEST engine it comes with from the factory is 175, largest is 240.

 

[jeffrayy]

Re: How to get a boat rated for HP

So is there a way to get one of those plates for your boat? The boat that I just bought does not have one and I need it in order to get boat insurance.

 

[180Fisherman]

Re: How to get a boat rated for HP

that formula is only a VERY rough estimate. According to that that formula my boat is rated for a max of 125. The SMALLEST engine it comes with from the factory is 175, largest is 240.

"Very rough" seem generous. In my case it's off 32% and even more so in your case. Seems "completely useless" would be a better way to describe that formula.

 

[QC]

Re: How to get a boat rated for HP

smokingcrater's sounds like an I/O. If so the CG rules would not apply . . .

 

[trendsetter240]

Re: How to get a boat rated for HP

I kinda have the oppostite situation.

I have a 150HP motor and I am looking for a boat to put it on. There is a Slickcraft SS170 listed locally for a really good price. I have a few questions.

Is the Grew that you have actually, verifiably the same boat as the Slickcraft SS170?

What is the width of the transom...as defined by the coast gaurd docoument tashasdaddy linked to?

What is the height of the transom? 20"?

The current owner of the boat local to me says that even with the 90 HP motor he has on it, it may be more power than neccessary.

That being said, I made some assumptions and ran through the calc:

L = 17
W = 7
Transom Height = 20"

(17x7x2)-90 = 148 ... 150 HP rating.

But, as has been said with assumptions....

Without an actual boat in front of me I can't be certain on this.

Yes the Grew boat is the same model as the Slickcraft SS170v.

The forumula comes out with 114HP as the max, the boat is more like 16.3ft X 6.25ft. Transom is 20". I belive my is a 1969 model though and the mesurements changed slightly for the different years.

 

[trendsetter240]

Re: How to get a boat rated for HP

Since I can't get a plate rating and at 400lbs the v6 150HP motor is too heavy for my boat so I am going to pass on it.

The other ss170's that I've seen on the net all have 70hp to 115hp motors hanging off the back. I guess I will just stick within that range for now.

Thanks for the comments!

 

[RotaryRacer]

Re: How to get a boat rated for HP

Thanks for the follow up.

It sounds like you have a good plan.