building xf20

[Freaknreakn]

Hey Mr. Paul,
I'm going to start fairing myself this weekend. Looking at your pics (great btw), did you wrap any cloth over your rub rail? I'm asking b/c I did but have a few spots to touch up and add cloth to the rub rail where it was short. I'm wondering about not doing it and covering it when I do bow, gunnel and decks. Will having fairing/primer on those areas affect the bond? Maybe someone from the board can chime in.

[MrPaul]

I didn't glass the rails yet. I'm going to tape the decks down so that should count for the glass on the rails. I would think that fairing compound or primer on the rails would affect bonding for the glass so mine are currently all wood. I dripped lots of compound on them in the fairing process so I have to sand them before I tape the decks on.

[MrPaul]

Been working on this boat.off and on for about 6 years. Lots of other things have come up. It's a center console with the front and rear casting decks. Anyways....it's almost done and i need to buy a motor. I think I built the boat pretty heavy and to make things heavier....my wife wants a leaning post and t top (180 extra pounds) I think it might need more horsepower than the 70 hp I had originally planned. I have scuper holes with clam shells 8" above the bottom of the boat. I worry about the scupers going below the waterline if I put a 115 on it. It's about 120 pounds more than the 70 hp + the extra weight from a bigger jack plate.

Also...the boat only has 1 layer of 1708 inside and out. I've got 4 stringers and the transom is thick (4 layers of 1/2 meranti + 1" Honduran mahogany clamping board (more weight). I've also put extra 1708 around the sides inside and out and at the bottom of the transom on the inside. I'm not worried about the transom strength. I am worried about the strength of the running surface with only 1 layer of 1708 2 layers of tape outside and 3 layers inside. With the 24 volt trolling motor a cranking battery and a house battery...that's 4 batteries. The fuel tank is 30 gallons under the console. It seems like a lot of weight for a 70 hp 4 stroke yamaha. I'll be happy if I can get 30 mph out of the boat. Will a 70 hp be enough??? If not...will the boat withstand a 115 with only 1 layer of 1708 on the bottom?

[fallguy1000]

The quality of the bottom laminate is all that matters.

If you did poor work, a 70hp will delam the bottom.

The only way for me to comment about the scuppers is to know the DWL dimension, not the distance off the bottom.

If you are 3" above DWL, then the boat can afford only a couple inches of immersion. But you can always plug the aft scuppers if you realize an issue.

I say go for higher hp, based on your info. Best of luck.

[MrPaul]

The lamination is well done but I don't know where the DWL is yet. I hope everything comes out right. It hasn't been as much work as your boat...but a lot of work none the less.

[TomW1]

Mr Paul most builders of the XF20 are happy with a 70HP motor. If you want me to I will use my calculators to check on that. There are a lot of things to be considered but the most important is to get correct the weight of the boat as it leaves the dock. There have been several XF20's built with a 70HP motor that achieve 30mph or more.

Tom

[Dr Pete]

Friend told me…”Have you ever heard anyone say they wished they had a slower boat or less motor?” I’ve got a 90 2 Stroke Yami on a heavy XF 20. Jack plate. Draft’s 6”. Top speed going downhill with a tailwind in smooth water is 30. I think 115 would be the way to go.

[MrPaul]

Hi, Pete, Tom,

I don't know what the weight of the boat is but I know I need to figure out how to weigh it. I'm thinking with the t-top and leaning post, the hull weight will be about 1150 lbs + batteries, fuel (29 gals), fishing equipment, and fisherman. I would like to go with a 70 but I'm having my doubts. In total with the console. I've used 19 sheets of 3/8 okume, 2 sheets of 1/2 meranti for the transom, 1 sheet of 1/4" okume for compartments under the hatches. My nesting was not great and I've probably had more waste than most. Id asume 15%. 1 layer of 1708 with a little extra on the sides and to beef up the transom. The deck is covered with 10 oz glass. I read Pete's posts about his xf with the 90 hp long ago. That was what made me think the 70 would not be enough. I'm also going to have to go with a 4 stroke. I want a new motor and that rules out any 2 stroke motors. My neighbor is a certified yamaha mechanic so yamaha is looking like my best choice.

Tom, based on the estimated weight.....what do you think? Will a 70 work and get me near 30mph? Pete had to go to a 90 and if I'm going that rought with a 4 stroke a 115 weighs the same.

I will find a way to weigh the boat once it's painted and fixed with all of the extras less the motor and jackplate.

[fallguy1000]

Most of these engines are build from the same block. Yamaha 90 and 115 are the same. So, all they do is bore out more for the 115.

So, when you make a motor decision; you look at categories of blocks.

Engines x,y,z all have the same block and so weights are all very close.

engines a,bc are a next size up and the weight increase is substantial

You can find out from the dealer the block classes, or research and write down weights and back into them.

For my boat, the 115 Yamaha and the 90 are in the same block class. But because my boat is a semi-planing form and I only wanted to achieve 20 knots, with the 115; we estimated up at around 25 knots and just didn't want to push her that hard. Keep in mind, speed changes forces on the hull. I was recently warned to stay below 15 kts in seas over 4' based on composites data.

I am getting 22 knots or so, so very pleased and it feels plenty fast for such a wide beast.

[MrPaul]

Your boat is a beast fallguy. I'm happy you got a respectable speed out of her. I'm hoping Tom gets back to me and tells me a 70 will work but I don't think ia 70 will get it on plane with 4 fishermen....let alone 30 mph. Maybe if I started hanging out with some smaller folks that would help but most of my fishing buddies are 200lbs and up.